Investments - Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	$ 22,268	$ 22,067
Allowance for Credit Losses	(1)	(4)
Net Amortized Cost	22,267	22,063
Gross Unrealized Gains	69	57
Gross Unrealized Losses	(1,433)	(1,840)
Fair Value	20,903	20,280
Supporting experience-rated products
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	4	3
Gross Unrealized Losses	(44)	(59)
Fair Value	600	609
U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,066	2,074
Allowance for Credit Losses	0	0
Net Amortized Cost	2,066	2,074
Gross Unrealized Gains	1	0
Gross Unrealized Losses	(159)	(182)
Fair Value	1,908	1,892
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,391	2,393
Allowance for Credit Losses	0	0
Net Amortized Cost	2,391	2,393
Gross Unrealized Gains	10	8
Gross Unrealized Losses	(91)	(129)
Fair Value	2,310	2,272
U.S. corporate securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	10,061	9,838
Allowance for Credit Losses	0	(3)
Net Amortized Cost	10,061	9,835
Gross Unrealized Gains	32	26
Gross Unrealized Losses	(703)	(903)
Fair Value	9,390	8,958
Foreign securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,761	2,780
Allowance for Credit Losses	(1)	(1)
Net Amortized Cost	2,760	2,779
Gross Unrealized Gains	17	15
Gross Unrealized Losses	(192)	(244)
Fair Value	2,585	2,550
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	863	845
Allowance for Credit Losses	0	0
Net Amortized Cost	863	845
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(79)	(89)
Fair Value	785	757
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	1,137	1,172
Allowance for Credit Losses	0	0
Net Amortized Cost	1,137	1,172
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(140)	(155)
Fair Value	998	1,018
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,969	2,940
Allowance for Credit Losses	0	0
Net Amortized Cost	2,969	2,940
Gross Unrealized Gains	7	6
Gross Unrealized Losses	(68)	(136)
Fair Value	2,908	2,810
Redeemable preferred securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	20	25
Allowance for Credit Losses	0	0
Net Amortized Cost	20	25
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(2)
Fair Value	$ 19	$ 23