Investments - Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	$ 22,102	$ 22,067
Allowance for Credit Losses	(1)	(4)
Net Amortized Cost	22,101	22,063
Gross Unrealized Gains	35	57
Gross Unrealized Losses	(1,735)	(1,840)
Fair Value	20,401	20,280
Supporting experience-rated products
Debt Securities, Available-for-sale [Line Items]
Gross Unrealized Gains	2	3
Gross Unrealized Losses	(63)	(59)
Fair Value	560	609
U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,092	2,074
Allowance for Credit Losses	0	0
Net Amortized Cost	2,092	2,074
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(171)	(182)
Fair Value	1,921	1,892
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,277	2,393
Allowance for Credit Losses	0	0
Net Amortized Cost	2,277	2,393
Gross Unrealized Gains	1	8
Gross Unrealized Losses	(151)	(129)
Fair Value	2,127	2,272
U.S. corporate securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	10,062	9,838
Allowance for Credit Losses	0	(3)
Net Amortized Cost	10,062	9,835
Gross Unrealized Gains	12	26
Gross Unrealized Losses	(879)	(903)
Fair Value	9,195	8,958
Foreign securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,621	2,780
Allowance for Credit Losses	(1)	(1)
Net Amortized Cost	2,620	2,779
Gross Unrealized Gains	9	15
Gross Unrealized Losses	(233)	(244)
Fair Value	2,396	2,550
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	833	845
Allowance for Credit Losses	0	0
Net Amortized Cost	833	845
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(103)	(89)
Fair Value	730	757
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	1,128	1,172
Allowance for Credit Losses	0	0
Net Amortized Cost	1,128	1,172
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(151)	(155)
Fair Value	977	1,018
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	3,069	2,940
Allowance for Credit Losses	0	0
Net Amortized Cost	3,069	2,940
Gross Unrealized Gains	13	6
Gross Unrealized Losses	(46)	(136)
Fair Value	3,036	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