Investments - Value of Other Securities Measured at Fair Value Based on Election of the Fair Value Option (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2025	Dec. 31, 2024
Debt and Equity Securities, FV-NI [Line Items]
Other bond securities	$ 743	$ 745
Equity securities	829	704
Fixed Maturities And Equity Securities
Debt and Equity Securities, FV-NI [Line Items]
Total	$ 1,572	$ 1,449
Fixed Maturities And Equity Securities \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	100.00%	100.00%
Fixed maturity securities
Debt and Equity Securities, FV-NI [Line Items]
Other bond securities	$ 743	$ 745
Fixed maturity securities \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	46.00%	51.00%
Fixed maturity securities \| Obligations of states, municipalities and political subdivisions
Debt and Equity Securities, FV-NI [Line Items]
Other bond securities	$ 51	$ 50
Fixed maturity securities \| Obligations of states, municipalities and political subdivisions \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	3.00%	3.00%
Fixed maturity securities \| Non-U.S. governments
Debt and Equity Securities, FV-NI [Line Items]
Other bond securities	$ 22	$ 24
Fixed maturity securities \| Non-U.S. governments \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	1.00%	2.00%
Fixed maturity securities \| Corporate debt
Debt and Equity Securities, FV-NI [Line Items]
Other bond securities	$ 258	$ 282
Fixed maturity securities \| Corporate debt \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	16.00%	19.00%
Fixed maturity securities \| Mortgage-backed, asset-backed and collateralized
Debt and Equity Securities, FV-NI [Line Items]
Other bond securities	$ 412	$ 389
Fixed maturity securities \| Mortgage-backed, asset-backed and collateralized \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	26.00%	27.00%
Fixed maturity securities \| RMBS
Debt and Equity Securities, FV-NI [Line Items]
Other bond securities	$ 99	$ 100
Fixed maturity securities \| RMBS \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	6.00%	7.00%
Fixed maturity securities \| CMBS
Debt and Equity Securities, FV-NI [Line Items]
Other bond securities	$ 42	$ 43
Fixed maturity securities \| CMBS \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	3.00%	3.00%
Fixed maturity securities \| CLO/ABS
Debt and Equity Securities, FV-NI [Line Items]
Other bond securities	$ 271	$ 246
Fixed maturity securities \| CLO/ABS \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	17.00%	17.00%
Equity securities
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 829	$ 704
Equity securities \| Investment Concentration Risk \| Investments
Debt and Equity Securities, FV-NI [Line Items]
Concentration risk (as a percent)	54.00%	49.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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