Investments - Debt Securities (Details) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	$ 22,838,000,000	$ 22,174,000,000
Allowance for Credit Losses	(42,000,000)	0
Net Amortized Cost	22,796,000,000	22,174,000,000
Gross Unrealized Gains	428,000,000	1,172,000,000
Gross Unrealized Losses	(726,000,000)	(106,000,000)
Fair Value	22,498,000,000	23,240,000,000
Supporting experience-rated products
Debt Securities, Available-for-sale [Line Items]
Allowance for Credit Losses	(4,000,000)	0
Gross Unrealized Gains	38,000,000	94,000,000
Gross Unrealized Losses	(13,000,000)	(2,000,000)
Fair Value	775,000,000	864,000,000
U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,333,000,000	2,349,000,000
Allowance for Credit Losses	0	0
Net Amortized Cost	2,333,000,000	2,349,000,000
Gross Unrealized Gains	21,000,000	70,000,000
Gross Unrealized Losses	(68,000,000)	(3,000,000)
Fair Value	2,286,000,000	2,416,000,000
States, municipalities and political subdivisions
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,526,000,000	2,947,000,000
Allowance for Credit Losses	0	0
Net Amortized Cost	2,526,000,000	2,947,000,000
Gross Unrealized Gains	37,000,000	148,000,000
Gross Unrealized Losses	(65,000,000)	(4,000,000)
Fair Value	2,498,000,000	3,091,000,000
U.S. corporate securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	10,005,000,000	9,093,000,000
Allowance for Credit Losses	0	0
Net Amortized Cost	10,005,000,000	9,093,000,000
Gross Unrealized Gains	261,000,000	682,000,000
Gross Unrealized Losses	(322,000,000)	(40,000,000)
Fair Value	9,944,000,000	9,735,000,000
Foreign securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	3,049,000,000	2,821,000,000
Allowance for Credit Losses	(42,000,000)	0
Net Amortized Cost	3,007,000,000	2,821,000,000
Gross Unrealized Gains	87,000,000	196,000,000
Gross Unrealized Losses	(95,000,000)	(24,000,000)
Fair Value	2,999,000,000	2,993,000,000
Residential mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	910,000,000	870,000,000
Allowance for Credit Losses	0	0
Net Amortized Cost	910,000,000	870,000,000
Gross Unrealized Gains	5,000,000	15,000,000
Gross Unrealized Losses	(48,000,000)	(10,000,000)
Fair Value	867,000,000	875,000,000
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	1,284,000,000	1,278,000,000
Allowance for Credit Losses	0	0
Net Amortized Cost	1,284,000,000	1,278,000,000
Gross Unrealized Gains	8,000,000	44,000,000
Gross Unrealized Losses	(67,000,000)	(12,000,000)
Fair Value	1,225,000,000	1,310,000,000
Other asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	2,706,000,000	2,791,000,000
Allowance for Credit Losses	0	0
Net Amortized Cost	2,706,000,000	2,791,000,000
Gross Unrealized Gains	8,000,000	14,000,000
Gross Unrealized Losses	(61,000,000)	(13,000,000)
Fair Value	2,653,000,000	2,792,000,000
Redeemable preferred securities
Debt Securities, Available-for-sale [Line Items]
Gross Amortized Cost	25,000,000	25,000,000
Allowance for Credit Losses	0	0
Net Amortized Cost	25,000,000	25,000,000
Gross Unrealized Gains	1,000,000	3,000,000
Gross Unrealized Losses	0	0
Fair Value	$ 26,000,000	$ 28,000,000