Fair Value - Reconciliations of Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Corporate bonds and other
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	$ 1,483	$ 1,278
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income	(3)
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI	(24)	21
Purchases	63	55
Sales
Settlements	(5)	(18)
Transfers into Level 3		15
Transfers out of Level 3
Balance at ending of period	1,514	1,351
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at March 31
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at March 31	(24)	21
States, municipalities and political subdivisions
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	45	42
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI	(1)	2
Purchases
Sales
Settlements
Transfers into Level 3
Transfers out of Level 3
Balance at ending of period	44	44
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at March 31
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at March 31	(1)	2
Asset-backed
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	998	876
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income	2	4
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI	(16)	1
Purchases	40	27
Sales
Settlements	(20)	(19)
Transfers into Level 3
Transfers out of Level 3	(49)
Balance at ending of period	955	889
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at March 31
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at March 31	(16)	1
Fixed maturities available-for-sale
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	2,526	2,196
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income	(1)	4
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI	(41)	24
Purchases	103	82
Sales	0	0
Settlements	(25)	(37)
Transfers into Level 3	0	15
Transfers out of Level 3	(49)	0
Balance at ending of period	2,513	2,284
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at March 31	0	0
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at March 31	(41)	24
Equity securities
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	33	20
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income	(1)	1
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI
Purchases
Sales
Settlements		(4)
Transfers into Level 3
Transfers out of Level 3
Balance at ending of period	32	17
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at March 31	(1)	(1)
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at March 31