Chubb Ltd

8. Unpaid losses and loss expenses

The following table presents a reconciliation of beginning and ending Unpaid losses and loss expenses:

(2)Relates to prior period loss reserve development only and excludes prior period development related to reinstatement premiums, expense adjustments, earned premiums, and A&H long-duration lines totaling $118 million and $71 million for the nine months ended September 30, 2024 and 2023, respectively.

Net unpaid losses and loss expenses increased $4,457 million for the nine months ended September 30, 2024, principally reflecting underlying exposure growth, net catastrophe losses, and the impact of a reinsurance commutation in connection with a large structured transaction during the first quarter, partially offset by the impact of favorable prior period development. The increase in net unpaid losses also reflected seasonality in our crop insurance business.

Prior Period Development

Prior period development (PPD) arises from changes to loss estimates recognized in the current year that relate to loss events that occurred in previous calendar years and excludes the effect of losses from the development of earned premium from previous accident years. Long-tail lines include lines such as workers' compensation, general liability, and financial lines; while short-tail lines include lines such as most property lines, energy, personal accident, and agriculture. The following table summarizes (favorable) and adverse PPD by segment:

Significant prior period movements by segment, principally driven by reserve reviews completed during each respective period, are discussed in more detail below. The remaining net development for long-tail lines and short-tail business for each segment and Corporate comprises numerous favorable and adverse movements across a number of lines and accident years, none of which is significant individually or in the aggregate.

North America Commercial P&C Insurance. Net favorable development for the three and nine months ended September 30, 2024, included $164 million and $310 million, respectively, from short-tail lines, primarily property and marine, driven by lower-than-expected loss development in the most recent accident years. The nine months ended September 30, 2024, also included favorable development from surety lines, due to lower-than-expected loss development. Long-tail lines experienced adverse development of $125 million and $79 million for the three and nine months ended September 30, 2024, respectively, which was the net of adverse development in casualty lines, predominantly commercial excess and umbrella and commercial auto liability, due to higher-than-expected loss development, partially offset by favorable development in workers' compensation due to lower-than-expected loss experience and our annual assessment of multi-claimant events, including industrial accidents.

Net favorable development for the three and nine months ended September 30, 2023, included $191 million and $279 million, respectively, from short-tail lines, primarily property and marine lines, mainly due to net lower-than-expected loss development impacting the most recent accident years. Development for the nine months ended September 30, 2023, also included favorable development in surety lines, due to lower-than-expected loss development.

Net adverse development of $107 million for the three months ended September 30, 2023, from long-tail lines included adverse development in casualty lines, predominantly commercial excess and umbrella lines, driven by higher-than-expected loss development, principally related to automobile exposures, partially offset by favorable development in workers' compensation due to lower-than-expected loss experience. Long-tail lines experienced net favorable development of $23 million for the nine months ended September 30, 2023, driven by workers’ compensation lines due to lower-than-expected loss development and our annual assessment of multi-claimant events, including industrial accidents, partially offset by adverse development in commercial excess and umbrella lines and commercial auto liability, both driven by higher-than-expected loss experience.

North America Personal P&C Insurance. Net favorable development for the three and nine months ended September 30, 2024 and 2023, was predominantly in homeowners, mainly due to lower-than-expected loss experience in the most recent accident years.

Overseas General Insurance. Net favorable development for the three months ended September 30, 2024, included $61 million from long-tail lines, primarily financial lines due to favorable loss emergence in accident years 2019 and 2020. Net favorable development for the nine months ended September 30, 2024, included $184 million from short-tail lines, primarily property and marine lines.

Net favorable development for the three and nine months ended September 30, 2023, included $52 million from long-tail lines, primarily financial lines due to favorable loss emergence in accident years 2019 and prior, partially offset by net adverse development in political risks. Net favorable development for the nine months ended September 30, 2023, included $201 million from short-tail lines, primarily property and marine, and A&H lines.

Corporate. Net adverse development for the three months ended September 30, 2024 and 2023, included adverse development resulting from our annual review of environmental liabilities. Net adverse development for the nine months ended September 30, 2024 and 2023, also included adverse development for molestation-related claims development.