Unum Group

We prepare our financial statements in accordance with GAAP. The preparation of financial statements in conformity with GAAP requires us to make estimates and assumptions that affect amounts reported in our financial statements and accompanying notes. Estimates and assumptions could change in the future as more information becomes known, which could impact the amounts reported and disclosed in our financial statements.

The accounting estimates deemed to be most critical to our financial position and results of operations are those related to the liability for future policy benefits, valuation of investments, pension and postretirement benefit plans, income taxes, and contingent liabilities. For additional information, refer to our significant accounting policies in Note 1 of the "Notes to Consolidated Financial Statements" contained herein in Item 8.

Liability for Future Policy Benefits

Liabilities for future policy benefits represent the cost of claims that we estimate we will eventually pay to our policyholders and the related expenses for our non interest-sensitive products. Liability for future policy benefits includes policy liabilities for claims not yet incurred and for claims that have been incurred or are estimated to have been incurred but not yet reported to us. Liability for future policy benefits equaled $36.8 billion and $40.0 billion at December 31, 2024 and 2023, or approximately 72.2 percent and 74.6 percent of our total liabilities, respectively. Liability for future policy benefits ceded to reinsurers was $7.0 billion and $7.8 billion at December 31, 2024 and 2023, respectively, and are reported as a reinsurance recoverable in our consolidated balance sheets.

Liabilities for future policy benefits are initially established in the same period in which we issue a policy, and equal the difference between projected future policy benefits and projected future premiums, allowing a margin for expenses and profit. The liabilities for future policy benefits build up and release over time, based on the emergence of cash flows, including premiums received and claims paid, and updated expectations for future cash flows.

Liabilities for future policy benefits are updated at each reporting date to reflect changes in the liability based on policy development over time, emerging experience, and any assumption updates required to maintain the best estimate basis for expected future cash flows as required by GAAP. These future policy benefit liabilities are based on actual known facts regarding the liability, such as the benefits available under the applicable policy, the covered benefit period, the age, and, as appropriate, the occupation and cause of disability of the claimant, as well as assumptions derived from our actual historical experience and expected future changes in experience for factors such as the claim duration, claim administration expenses, discount rate, policy benefit offsets, including those for social security and other government-based welfare benefits. The liability for future policy benefits also includes the liabilities for incurred claims.

Future policy benefit liabilities primarily relate to our traditional long-duration products which include our group, individual disability and certain of our voluntary benefits products in our Unum US segment; group, individual disability and life products in our Unum International segment; certain of our voluntary benefits products in our Colonial Life segment; and long-term care and certain of our other products in our Closed Block segment.

In calculating the liability for future policy benefits, our long-duration contracts are grouped into cohorts by product type and contract issue year. Liabilities for future policy benefits for claims not yet incurred are generally determined using the net premium model as prescribed by GAAP. At each reporting period, the liability for future policy benefits is remeasured at the current discount rate with the change recorded in other comprehensive income.

The calculation of the liability for future policy benefits involves numerous assumptions including discount rate, lapses, mortality, and morbidity. Certain product lines may utilize additional assumptions in calculating the liability for future policy benefits in addition to those listed above such as premium rate increases for long-term care, benefit offsets for Unum US long-term disability, claim costs for Unum US voluntary benefits and Colonial Life, and inflation-linked benefits for Unum UK group disability and group life. Claim costs capture the combined effect of the incidence rate, the expected level of benefit to be paid, and the claim resolution rate. Cash flow assumptions are reviewed and updated, as needed, at least annually. Assumptions may be updated more frequently, if necessary, based on trending experience.

On a quarterly basis, cohort level cash flow measures are updated based on the emergence of actual experience. The updated cash flows, based on experience emergence and any assumption updates, are used to determine the updated net premiums, the portion of the gross premium required to provide for all benefits and expenses, excluding acquisition costs or any costs that are required to be charged to expense as incurred. The updated net premium ratio is used to calculate the updated liability for future policy benefits as of the beginning of year, at the original discount rate. To the extent the present value of future benefits and expenses exceeds the present value of future gross premiums, an immediate charge is recognized in net income, such that net premiums are set equal to gross premiums. Future policy benefit liabilities are floored at zero at the cohort level in situations where the liabilities for future policy benefits are less than zero. The change in the liability for future policy benefits, at the original discount rate, as of the beginning of the period, resulting from cash flow changes, including changes in cash flow assumptions, is reflected as the change in benefits - remeasurement gain or loss in the consolidated statements of income. The impact of all other changes in the liability for future policy benefits are reflected as policy benefits in the consolidated statements of income.

Key Assumptions

The calculation of the liability for future policy benefits involves numerous assumptions, but the primary assumptions used to calculate the liability are (1) the discount rate, (2) the claim resolution rate, (3) the claim incidence rate, and (4) policyholder lapse and mortality:

1. Thediscount rate, which is used in calculating the liability for future policy benefits, is the interest rate that we use to discount future cash flows including premium and claim payments to determine the present value. A higher discount rate produces a lower reserve. If the discount rate is higher than our future investment returns, our invested assets will not earn enough investment income to support our future claim payments. The original discount rates are initially set at the transition date of ASU 2018-12, which was January 1, 2021, for policies originally issued before the transition date, or at the policy issuance date, for policies issued on or after the transition date. For policies issued on or after the transition date, the original discount rate assumptions reflect an upper-medium grade (low-credit risk) fixed-income instrument yield based on the currency in which the liabilities are assumed and matched to the duration of the insurance liabilities. For all cohorts, the liability is then remeasured at each reporting period using the current discount rate reflective of an upper-medium grade fixed-income instrument. We primarily utilize a forward curve which is derived from the underlying spot curve using interpolation to develop an ultimate forward rate.

2. Theclaim resolution rate is the probability that a disability or long-term care claim will close due to recovery or death of the insured and it is used to estimate how long benefits will be paid for a claim. Estimated resolution rates that are set too high will result in liabilities that are lower than they need to be to pay the claim benefits over time. Claim resolution assumptions involve many factors, including the cause of disability, the policyholder's age, the type of contractual benefits provided including benefit elections, and the time since initial disability. We primarily use our own claim experience to develop our claim resolution assumptions. These assumptions are established for the probability of death and the probability of recovery from disability. Our studies incorporate actual claim resolution experience over a number of years and consider any observed trends over the study period. We also consider any expected future changes in claim resolution experience.

3. The incidence rate is the rate at which new claims are submitted to us. The incidence rate is affected by many factors, including the age of the insured, the insured's occupation or industry, the benefit plan design, and certain external factors such as consumer confidence and levels of unemployment. We establish our incidence assumption using a historical review of actual incidence results along with an outlook of future incidence expectations.

4. Policyholder lapse and mortality assumptions reflect the probability that insureds’ coverage is discontinued due to lapsation or death of the insured. For our life insurance products, mortality assumptions also reflect the probability that a benefit payment occurs. These rates are affected by many factors, including the age of the insured, the insured's occupation or industry, the benefit plan design, and the length of time from policy or certificate issue to valuation date. We establish our mortality and lapse assumptions using a historical review of actual results along with an outlook of future expectations.

Establishing liability for future policy benefit assumptions is complex and involves many factors. Liabilities for future policy benefits, particularly for policies offering insurance coverage for long-term disabilities and long-term care, are dependent on numerous assumptions other than just those presented in the preceding discussion. The impact of internal and external events, such as changes in claims operational procedures, economic trends such as the rate of unemployment and the level of consumer confidence, the emergence of new diseases, new trends and developments in medical treatments, and legal trends and legislative changes, including changes to social security and other government-based welfare benefits programs which provide policy benefit offsets, among other factors, will influence claim incidence rates, claim resolution rates, and claim costs. In addition, for policies offering coverage for disability or long-term care at advanced ages, the level and pattern of mortality rates at advanced ages will impact overall benefit costs. Reserve assumptions differ by product line and by policy type within a product line. Additionally, in any period and over time, our actual experience may have a positive or negative variance from our long-term assumptions, either singularly or collectively, and these variances may offset each other. We review our assumptions at least annually with a long-term view of our expected experience over the life of a block of business rather than test just one or a few assumptions independently that may be aberrant over a short period of time. Based on this review, we update our assumptions to reflect our current best estimates. Therefore, while it is possible to evaluate the sensitivity of overall results in our liability for future policy benefits based upon a change in each individual assumption, the actual impacts of changes to a variety of underlying assumptions must be considered in the aggregate by product line in order to judge the overall potential implications to the liability for future policy benefits. The following sections present the impacts of our most recent cash flow assumption reviews and an overview of our trend analysis for key assumptions and the results of variability in our assumptions, in aggregate, for the liabilities for future policy benefits which we believe are reasonably possible to have a material impact on our future financial results if actual claims yield a materially different amount than what we currently expect and have reserved for, either favorable or unfavorable.

Cash Flow Assumption Review

Our cash flow assumption reviews during the years ended December 31, 2024, 2023, and 2022 resulted in the following impacts to income before income tax as a result of updating certain assumptions related to the liability for future policy benefits:

2024 Significant Cash Flow Assumption Updates:

The cash flow assumption updates in our Unum US group long-term disability product line reduced our liability for future policy benefits by $90.0 million, due primarily to claim resolution assumptions driven by favorable claim recovery trends.

The cash flow assumption updates in our Unum US individual disability product line reduced our liability for future policy benefits by $52.8 million, due primarily to favorable claim incidence trends.

The cash flow assumption updates in our Colonial Life segment reduced our liability for future policy benefits by $46.0 million, due primarily to improved claim cost assumptions.

The cash flow assumption updates in our Closed Block segment were primarily driven by the long-term care product line which reduced our liability for future policy benefits by $174.1 million, due primarily to an increase to expected premium rate increase approvals within our existing premium rate increase program, partially offset by lower expected persistency on group policies.

2023 Significant Cash Flow Assumption Updates:

The cash flow assumption updates in our Unum US group long-term disability product line reduced our liability for future policy benefits by $121.0 million, due primarily to sustained improvement in claim recovery trends.

The cash flow assumption updates in our Colonial Life segment reduced our liability for future policy benefits by $80.7 million, due primarily to improvement in certain of our claim cost assumptions and increased policyholder lapse rates.

The cash flow assumption updates in our Closed Block segment were primarily driven by the long-term care product line which increased our liability for future policy benefits by $368.1 million, due primarily to lower expectations for active policy lapse and mortality assumptions, partially offset by an increase to expected premium rate increase approvals within our existing premium rate increase program.

2022 Significant Cash Flow Assumption Updates:

The cash flow assumption updates in our Unum US group long-term disability product line and our waiver of premium benefits for our Unum US group life product line reduced our liability for future policy benefits by $121.0 million and $34.0 million, respectively, due primarily to sustained improvement in claim recovery trends, partially offset by lower social security benefit offsets for our group long-term disability product line.

The cash flow assumption updates in our Colonial Life segment reduced our liability for future policy benefits by $55.2 million, due primarily to improvement in certain of our claim cost assumptions.

The cash flow assumption updates in our Closed Block segment were primarily driven by the all other product line. The impact to income before income tax for this product line was $6.8 million and related to the small block of retained individual disability business. However, there were also updates to the mortality assumptions for the advanced age portion of our individual disability claimant population which was included in the block ceded as a part of the Closed Block individual disability reinsurance transaction with Commonwealth Annuity and Life Insurance Company. We increased our liability for future policy benefits by $196.0 million as a result of the assumption updates related to the ceded advanced age claimant block with a corresponding increase in our consolidated balance sheet as a reinsurance recoverable.

Trends in Key Assumptions

Generally, we do not expect our mortality and morbidity claim incidence trends or our persistency trends to change significantly in the short-term, and to the extent that these trends do change, we expect those changes to be gradual over a longer period of time. We have historically experienced an increase in our group long-term disability morbidity claim incidence trends during and following a recessionary period and believe claim incidence trends may continue to somewhat follow general economic conditions and demographics of the general workforce.

The long-term discount rates underlying our liabilities are reflective of rates based on the issue year of the cohort or rates underlying the liabilities at transition to the updated accounting basis as prescribed by ASU 2018-12. The discount rate assumption for new cohorts, after the transition date, is based on the interest rate of an upper-medium grade fixed-income instrument for that cohort period.

Our claim resolution rate assumption used in determining the liability for future policy benefits is our expectation of the resolution rate we will experience over the life of the block of business and will vary from actual experience in any one period, both favorably and unfavorably. Claim resolution rates are very sensitive to operational and environmental changes and have a greater chance of significant variability in a shorter period of time than our other reserve assumptions. These rates are reviewed on a quarterly basis for the death and recovery components separately. While claim resolution rates in our Unum US group long-term disability product line have shown some variability over the last several years, they have exhibited an increasing trend.

Sensitivity Analysis

We monitor our key assumptions and test the sensitivity of our liability for future policy benefits under a range of scenarios. This sensitivity analysis is completed at least annually and was last completed as of December 31, 2024 for our product lines with a higher level of estimation uncertainty and utilizes the liability for future policy benefits valued at the original discount rate. See "Quantitative and Qualitative Disclosures about Market Risk" contained herein in Item 7A for information regarding the sensitivity of the current discount rate used to remeasure the liability for future policy benefits at each reporting date.

In our estimation, scenarios based on certain variations in each of our assumptions for our Unum US group long-term disability product line could produce a change of approximately $100 million which represents 2.1 percent of our Unum US group disability liability for future policy benefits balance. Of the assumptions impacting the estimated change in the liability for future policy benefits, the largest contributor is the claim resolution rate for which we assumed a change of approximately 10 percent.

In our estimation, scenarios based on certain possible variations in each of our assumptions for our Colonial Life segment could produce a change of approximately $60 million which represents 3.2 percent of our Colonial Life liability for future policy benefits balance. Of the assumptions impacting the estimated change in the liability for future policy benefits, the largest contributor is the claim costs, for which we assumed a change of approximately 10 percent.

We also consider variability in our assumptions related to the long-term care liability for future policy benefits. In our estimation, scenarios based on certain variations in each of our assumptions could produce potential results as illustrated in the chart below. The liability for future policy benefits for long-term care is based upon a number of key assumptions, and each assumption has various factors which may impact the long-term outcome. Key assumptions with respect to active policy lapses and mortality, claim incidence and resolutions, and future premium rate increases must incorporate extended views of expectations for many years into the future. The liability for future policy benefits is highly sensitive to these estimates. Key assumptions and related impacts are also heavily interrelated in both their outcome and in their effects on the liability for future policy benefits. For example, changes in the view of morbidity and mortality might be mitigated by either potential future premium rate increases and/or morbidity improvements due to general improvement in health and/or medical breakthroughs. There is a potentially wide range of outcomes for each assumption and in totality. As a result, and given the size of the long-term care liability for future policy benefits in relation to the total liability for future policy benefits, our sensitivity analysis for long-term care reflects the potential impact to the present value of gross liability cash flows for future policy benefits for updates to our key assumptions. The sensitivity analysis related to our key assumptions for the long-term care liability for future policy benefits is as shown below. The impact of changes to these assumptions would partially be reflected in the period in which the assumptions are updated and partially across future periods. Given the significant changes in certain assumptions, the below sensitivity analysis was completed as of the beginning of the third quarter of 2024 at which point the most recent assumption update review occurred.

The impact to current period liability for future benefits would be smaller in magnitude than the present value of gross liability for future policy benefits cash flows due to the updating of the net premium ratio. The current period liability for future policy benefits impact may be asymmetrical (i.e. larger for the unfavorable scenario) for some sensitivities if the assumption update causes the net premium ratio to be capped at 100 percent for any given cohort.

We believe that these sensitivities provide a reasonable estimate of the possible changes in liability for future policy benefit balances for those product lines where we believe it is possible that variability in the assumptions, in the aggregate, could result in a material impact on our liability for future policy benefit levels, but we record our liability for future policy benefits based on our long-term best estimate for our cohorts and these assumptions are reviewed and updated annually to reflect the current best estimates. Product lines that have long-term claim payout periods have a greater potential for significant variability in claim costs, either positive or negative. We closely monitor emerging experience and use these results to inform our view of long-term assumptions.

Fair Value of Investments

All of our fixed maturity securities, which are classified as available-for-sale, and all of our unrestricted equity securities are reported at fair value. Our derivative financial instruments, including certain derivative instruments embedded in other contracts, are reported as either assets or liabilities and measured at fair value. We report our investments in private equity partnerships at our share of the partnerships' net asset value or its equivalent (NAV), as a practical expedient for fair value.

Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date and therefore represents an exit price, not an entry price. The exit price objective applies regardless of our intent and/or ability to sell the asset or transfer the liability at the measurement date. We generally use valuation techniques consistent with the market approach, and to a lesser extent, the income approach. The market approach uses prices and other relevant information from market transactions involving identical or comparable assets or liabilities and the income approach converts future amounts, such as cash flows or earnings, to a single present value amount, or a discounted amount. We believe the market approach valuation technique provides more observable data than the income approach, considering the types of investments we hold.

The degree of judgment utilized in measuring the fair value of financial instruments generally correlates to the level of pricing observability. Financial instruments with readily available active quoted prices or for which fair value can be measured from actively quoted prices in active markets generally have more pricing observability and less judgment utilized in measuring fair value. The market sources from which we obtain or derive the fair values of our assets and liabilities carried at market value include quoted market prices for actual trades, price quotes from third party pricing vendors, price quotes we obtain from outside brokers, discounted cash flow, and observable prices for similar publicly traded or privately traded issues that incorporate the credit quality and industry sector of the issuer. Our fair value measurements could differ significantly based on the valuation technique and available inputs.

Inputs to valuation techniques refer broadly to the assumptions that market participants use in pricing assets or liabilities, including assumptions about risk, for example, the risk inherent in a particular valuation technique used to measure fair value and/or the risk inherent in the inputs to the valuation technique. We use observable and unobservable inputs in measuring the fair value of our financial instruments. Observable inputs are inputs that reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from independent sources. Unobservable inputs are developed based on the best information available in the circumstances, and reflect our evaluation of the assumptions market participants would use in pricing the asset or liability.

Certain of our investments do not have readily determinable market prices and/or observable inputs or may at times be affected by the lack of market liquidity. For these securities, we use internally prepared valuations, including valuations based on estimates of future profitability, to estimate the fair value. Additionally, we may obtain prices from independent third-party brokers to aid in establishing valuations for certain of these securities. Key assumptions used by us to determine fair value for these securities include risk-free interest rates, risk premiums, performance of underlying collateral (if any), and other factors involving significant assumptions which may or may not reflect those of an active market.

As of December 31, 2024, approximately 11.7 percent of our fixed maturity securities were categorized as Level 1, 87.9 percent as Level 2, and 0.4 percent as Level 3. Level 1 is the highest category of the three-level fair value hierarchy classification wherein inputs are unadjusted and represent quoted prices in active markets for identical assets or liabilities. The Level 2 category includes assets or liabilities valued using inputs (other than those included in the Level 1 category) that are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument's anticipated life. The Level 3 category is the lowest category of the fair value hierarchy and reflects the judgment of management regarding what market participants would use in pricing assets or liabilities at the measurement date using unobservable inputs to extrapolate an estimated fair value.

Rapidly changing credit and equity market conditions can materially impact the valuation of securities, and the period to period changes in value can vary significantly.

See "Quantitative and Qualitative Disclosures about Market Risk" for information regarding the sensitivity of the estimated fair value for fixed maturity securities contained herein in Item 7A. See Note 2 of the "Notes to Consolidated Financial Statements" contained herein in Item 8.

Investment Credit Losses

One of the significant estimates related to investments is our credit loss valuation. In determining when a decline in fair value below amortized cost of a fixed maturity security represents a credit loss, we evaluate the following factors:

•Whether we expect to recover the entire amortized cost basis of the security

•Whether we intend to sell the security or will be required to sell the security before the recovery of its amortized cost basis

•Whether the security is current as to principal and interest payments

•The significance of the decline in value

•Current and future business prospects and trends of earnings

•The valuation of the security’s underlying collateral

•Relevant industry conditions and trends relative to their historical cycles

•Market conditions

•Rating agency and governmental actions

•Bid and offering prices and the level of trading activity

•Adverse changes in estimated cash flows for securitized investments

•Changes in fair value subsequent to the balance sheet date

•Any other key measures for the related security

We evaluate available information, including the factors noted above, both positive and negative, in reaching our conclusions. In particular, we also consider the strength of the issuer’s balance sheet, its debt obligations and near term funding requirements, cash flow and liquidity, the profitability of its core businesses, the availability of marketable assets which could be sold to increase liquidity, its industry fundamentals and regulatory environment, and its access to capital markets. Although all available and applicable factors are considered in our analysis, our expectation of recovering the entire amortized cost basis of the security, whether we intend to sell the security, whether it is more likely than not we will be required to sell the security before recovery of its amortized cost, and whether the security is current on principal and interest payments are the most critical factors in determining whether a credit loss is possible. The significance of the decline in value is also an important factor, but we generally do not record a credit loss based solely on this factor, since often other more relevant factors will impact our evaluation of a security.

While determining whether a credit loss exists is a judgmental area, we utilize a formal, well-defined, and disciplined process to monitor and evaluate our fixed income investment portfolio, supported by issuer specific research and documentation as of the end of each period. The process results in a thorough evaluation of investments and the recording of credit losses on a timely basis for investments determined to have credit loss.

We use a comprehensive rating system to evaluate the investment and credit risk of our mortgage loans and to identify specific properties for inspection and reevaluation. We estimate an allowance for credit losses that we expect to incur over the life of our mortgage loans using a probability of default method. For each loan, we estimate the probability that the loan will default before its maturity (probability of default) and the amount of the loss if the loan defaults (loss given default). These two factors result in an expected loss percentage that is applied to the amortized cost of each loan to determine the expected credit loss. Mortgage loans are reported at amortized cost less the allowance for expected credit losses with the change in expected credit losses recognized as an investment gain or loss in our consolidated statements of income.

There are a number of significant risks inherent in the process of monitoring our investments for credit losses and determining when and if a credit loss exists. These risks and uncertainties include the following possibilities:

•The assessment of a borrower's ability to meet its contractual obligations will change.

•The economic outlook, either domestic or foreign, may be less favorable or may have a more significant impact on the borrower than anticipated, and as such, the investment may not recover in value.

•New information may become available concerning the security, such as disclosure of accounting irregularities, fraud, or corporate governance issues.

•Significant changes in credit spreads may occur in the related industry.

•Significant increases in interest rates may occur and may not return to levels similar to when securities were initially purchased.

•Adverse rating agency actions may occur.

See Notes 1 and 3 of the "Notes to Consolidated Financial Statements" contained herein in Item 8.

Pension and Postretirement Benefit Plans

We sponsor several defined benefit pension and other postretirement benefit (OPEB) plans for our employees, including non-qualified pension plans. The U.S. qualified and non-qualified defined benefit pension plans comprise the majority of our total benefit obligation and benefit cost. We maintain a separate defined benefit plan for eligible employees in our U.K. operation. The U.S. defined benefit pension plans were frozen and closed to new entrants on December 31, 2013, the OPEB plan was frozen and closed to new entrants on December 31, 2012, and the U.K. plan was frozen and closed to new entrants on December 31, 2002.

Assumptions

Our net periodic benefit costs and the value of our benefit obligations for these plans are determined based on a set of economic and demographic assumptions that represent our best estimate of future expected experience. Major assumptions used in accounting for these plans include the expected discount (interest) rate, the long-term rate of return on plan assets, and mortality rates. We also use, as applicable, expected increases in compensation levels and a weighted average annual rate of increase in the per capita cost of covered benefits, which reflects a health care cost trend rate, and the U.K. plan also uses expected cost of living increases to plan benefits.

The assumptions chosen for our pension and OPEB plans are reviewed annually, using a December 31 measurement date for each of our plans unless we are required to perform an interim remeasurement. The discount rate, expected long-term rate of return, and mortality rate assumptions have the most significant effect on our net periodic benefit costs associated with these plans. In addition to the effect of changes in our assumptions, the net periodic cost or benefit obligation under our pension and OPEB plans may change due to factors such as plan amendments, actual experience being different from our assumptions, special benefits to terminated employees, and/or changes in benefits provided under the plans.

•Discount rate - This interest assumption is based on the yield derived from a portfolio of high quality fixed income corporate debt instruments that reasonably match the timing and amounts of projected future benefits for each of our retirement-related benefit plans. The rate is determined at the measurement date.

•Long-term rate of return - This assumption is selected from a range of probable return outcomes from an analysis of the asset portfolio. The market-related value as it relates to our estimate of long-term rate of return equals the fair value of plan assets, determined as of the measurement date. The return on plan assets recognizes all asset gains and losses, including changes in fair value, through the measurement date. Our expectations for the future investment returns of the asset categories are based on a combination of historical market performance, evaluations of investment forecasts obtained from external consultants and economists, and current market yields. The expected return for the total portfolio is calculated based on the plan's strategic asset allocation. The actual rate of return on plan assets is determined based on the fair value of the plan assets at the beginning and the end of the period, adjusted for contributions and benefit payments. A lower long-term rate of return on plan assets increases our net periodic benefit cost.

Investment risk is measured and monitored on an ongoing basis through annual liability measurements, periodic asset/liability studies, and quarterly investment portfolio reviews. Risk tolerance is established through consideration of plan liabilities, plan funded status, and corporate financial condition. We believe our investment portfolios are well diversified by asset class and sector, with no undue risk concentrations in any one category. See Note 11 of the "Notes to Consolidated Financial Statements" contained herein in Item 8 for further discussion of the investment portfolios for our plans.

•Mortality rate - This assumption reflects our best estimate, as of the measurement date, of the life expectancies of plan participants in order to determine the expected length of time for benefit payments. We derive our assumptions from industry mortality tables.

The weighted average assumptions used in the measurement of our net periodic benefit costs for the years ended December 31 are as follows:

The following illustrates the sensitivity of the below items to a 50 basis point change in the discount rate or the expected long-term rate of return on plan assets:

Benefit Obligation and Fair Value of Plan Assets

During 2024, the fair value of plan assets in our U.S. qualified defined benefit pension plan decreased from $1,295.9 million to $1,241.6 million, or 4.2 percent, due to benefits and expenses paid, partially offset by a positive return on assets which resulted in a gain of approximately 2.1 percent. During 2024, the fair value of plan assets in our U.K. plan decreased from £114.2 million to £100.1 million, or 12.3 percent, due primarily to an unfavorable return on assets which resulted in a loss of approximately 14.1 percent. Although our rate of return on plan assets for 2024 differed from our assumptions used in the measurement of our net periodic benefit costs, we believe our assumptions appropriately reflect the impact of the current economic environment and our expectations for the future investment returns based on the plan's asset allocation.

The fair value of plan assets in our OPEB plan was $7.9 million and $8.2 million at December 31, 2024 and 2023, respectively. These assets represent life insurance contracts to fund the life insurance benefit portion of our OPEB plan. Our OPEB plan represents a non-vested, non-guaranteed obligation, and current regulations do not require specific funding levels for these benefits, which are comprised of retiree life, medical, and dental benefits. It is our practice to use general assets to pay medical and dental claims as they come due in lieu of utilizing plan assets for the medical and dental benefit portions of our OPEB plan.

The U.S. qualified defined benefit pension plan was in an underfunded position of $120.1 million and $116.2 million at December 31, 2024 and December 31, 2023, respectively. This year-over-year change was due primarily to an unfavorable return on plan assets compared to the assumption, mostly offset by the decrease in the benefit obligation due to the increase in discount rate. The U.K. plan was in an underfunded position of £21.4 million and £21.2 million at December 31, 2024 and 2023, respectively.

As of December 31, 2024, our pension and OPEB plans have an aggregate unrecognized net actuarial loss of $566.5 million and an unrecognized prior service credit of $1.4 million, which together represent the cumulative liability and asset gains and losses as well as the portion of prior service credits that have not been recognized in pension expense. The unrecognized net actuarial loss for our pension plans, which is $587.7 million at December 31, 2024, will be amortized over the average remaining life expectancy of the plan, which is approximately 23 years for the U.S. plans and 28 years for the U.K. plan, to the extent that it exceeds the 10 percent corridor, as described below. The unrecognized net actuarial gain of $21.2 million for our OPEB plan will be amortized over the average remaining life expectancy of the plan, estimated at 12 years, to the extent the gain is outside of the corridor. The corridor for the pension and OPEB plans is established based on the greater of 10 percent of the plan assets or 10 percent of the benefit obligation. At December 31, 2024, $344.1 million of the actuarial loss was outside of the corridor for the U.S. plans and £61.1 million was outside of the corridor for the U.K. plan. At December 31, 2024, $14.0 million of the actuarial gain was outside of the corridor for the OPEB plan.

The amortization of the unrecognized actuarial gain or loss and the unrecognized prior service credit is a component of our net periodic benefit cost and equaled $16.3 million, $7.0 million, and $15.5 million in 2024, 2023, and 2022, respectively.

See Note 11 of the "Notes to Consolidated Financial Statements" contained herein in Item 8 for further discussion.

Income Taxes

We provide for federal, state, and foreign income taxes currently payable, as well as those deferred due to temporary differences between the financial reporting and tax bases of assets and liabilities. Our accounting for income taxes represents our best estimate of various events and transactions. The calculation of our tax liabilities involves dealing with uncertainties in the application of complex tax laws in a multitude of jurisdictions, both domestic and foreign. The amount of income taxes we pay is subject to ongoing audits in various jurisdictions, and a material assessment by a governing tax authority could affect profitability.

We record a valuation allowance to reduce deferred tax assets to the amount that is more likely than not to be realized. Significant judgment is required in determining valuation allowances. In evaluating the ability to recover deferred tax assets, we consider all available positive and negative evidence including past operating results, the existence of cumulative losses in the most recent years, forecasted earnings, future taxable income, and prudent and feasible tax planning strategies. We consider our investment strategies when evaluating the ability to recover deferred tax assets on unrealized losses on investments. In the event we determine that we more likely than not will not be able to realize all or part of our deferred tax assets in the future, an increase to the valuation allowance is recorded in the period such determination is made. Likewise, if it is later determined that it is more likely than not that those deferred tax assets will be realized, the previously provided valuation allowance is reversed.

In establishing a liability for unrecognized tax benefits, assumptions are made in determining whether, and to what extent, a tax position may be sustained. GAAP prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of tax positions taken or expected to be taken in income tax returns. The evaluation of a tax position is a two step process. The first step is to determine whether it is more likely than not that a tax position will be sustained upon examination based on the technical merits of the position. The second step is to measure a position that satisfies the recognition threshold at the largest amount of benefit that is greater than 50 percent likely of being realized upon ultimate settlement. Tax positions that previously failed to meet the more likely than not threshold but that now satisfy the recognition threshold are recognized in the first subsequent financial reporting period in which that threshold is met. Previously recognized tax positions that no longer meet the more likely than not recognition threshold are derecognized in the first subsequent financial reporting period in which that threshold is no longer met. If a previously recognized tax position is settled for an amount that is different from the amount initially measured, the difference will be recognized as a tax benefit or expense in the period the settlement is effective.

Changes in tax laws, tax regulations, or interpretations of such laws or regulations, could have an impact on our provision for income tax and our effective tax rate, which could significantly affect the amounts reported in our financial statements.

See "Regulation" contained herein in Item 1. See Note 9 of the "Notes to Consolidated Financial Statements" contained herein in Item 8.

Contingent Liabilities

On a quarterly basis, we review relevant information with respect to litigation and contingencies to be reflected in our consolidated financial statements. An estimated loss is accrued when it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. It is possible that our results of operations or cash flows in a particular period could be materially affected by an ultimate unfavorable outcome of pending litigation or regulatory matters depending, in part, on our results of operations or cash flows for the particular period. See Note 16 of the "Notes to Consolidated Financial Statements" contained herein in Item 8.

Accounting Developments

For information on new accounting standards and the impact, if any, on our financial position or results of operations, see Note 1 of the "Notes to Consolidated Financial Statements" contained herein in Item 8.