Investments - Debt Securities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	$ 22,282	$ 22,067
Allowance for Credit Losses	0	(4)
Net Amortized Cost	22,282	22,063
Gross Unrealized Gains	267	57
Gross Unrealized Losses	(836)	(1,840)
Fair Value	21,713	20,280
U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,071	2,074
Allowance for Credit Losses	0	0
Net Amortized Cost	2,071	2,074
Gross Unrealized Gains	19	0
Gross Unrealized Losses	(54)	(182)
Fair Value	2,036	1,892
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,219	2,393
Allowance for Credit Losses	0	0
Net Amortized Cost	2,219	2,393
Gross Unrealized Gains	31	8
Gross Unrealized Losses	(35)	(129)
Fair Value	2,215	2,272
U.S. corporate securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	10,156	9,838
Allowance for Credit Losses	0	(3)
Net Amortized Cost	10,156	9,835
Gross Unrealized Gains	133	26
Gross Unrealized Losses	(446)	(903)
Fair Value	9,843	8,958
Foreign securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,593	2,780
Allowance for Credit Losses	0	(1)
Net Amortized Cost	2,593	2,779
Gross Unrealized Gains	41	15
Gross Unrealized Losses	(122)	(244)
Fair Value	2,512	2,550
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	862	845
Allowance for Credit Losses	0	0
Net Amortized Cost	862	845
Gross Unrealized Gains	8	1
Gross Unrealized Losses	(60)	(89)
Fair Value	810	757
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	1,066	1,172
Allowance for Credit Losses	0	0
Net Amortized Cost	1,066	1,172
Gross Unrealized Gains	9	1
Gross Unrealized Losses	(100)	(155)
Fair Value	975	1,018
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	3,294	2,940
Allowance for Credit Losses	0	0
Net Amortized Cost	3,294	2,940
Gross Unrealized Gains	26	6
Gross Unrealized Losses	(18)	(136)
Fair Value	3,302	2,810
Redeemable preferred securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	21	25
Allowance for Credit Losses	0	0
Net Amortized Cost	21	25
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(2)
Fair Value	20	23
Supporting experience- rated products
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	10	3
Gross Unrealized Losses	(28)	(59)
Fair Value	$ 592	$ 609