Investments - Gross Unrealized Appreciation (Depreciation) on Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 10,634	$ 10,842
Allowance for Credit Loss	(45)	(44)
Unrealized Appreciation	73	133
Unrealized Depreciation	(1,123)	(1,059)
Fair Value	9,539	9,872
Federal government and agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	278	292
Allowance for Credit Loss	0	0
Unrealized Appreciation	19	32
Unrealized Depreciation	(14)	(12)
Fair Value	283	312
State and local government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	41	43
Allowance for Credit Loss	0	0
Unrealized Appreciation	0	0
Unrealized Depreciation	(3)	(2)
Fair Value	38	41
Foreign government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	373	375
Allowance for Credit Loss	0	0
Unrealized Appreciation	4	11
Unrealized Depreciation	(21)	(21)
Fair Value	356	365
Corporate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,548	9,742
Allowance for Credit Loss	(45)	(44)
Unrealized Appreciation	50	89
Unrealized Depreciation	(1,037)	(981)
Fair Value	8,516	8,806
Mortgage and other asset-backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	394	390
Allowance for Credit Loss	0	0
Unrealized Appreciation	0	1
Unrealized Depreciation	(48)	(43)
Fair Value	$ 346	$ 348