Investments - Gross Unrealized Appreciation (Depreciation) on Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 22,273	$ 21,909
Allowance for Credit Loss	(40)	0
Unrealized Appreciation	2,547	1,876
Unrealized Depreciation	(107)	(30)
Fair Value	24,673	23,755
Run-Off Settlement Annuity Business
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,147	2,229
Allowance for Credit Loss	(9)	0
Unrealized Appreciation	828	740
Unrealized Depreciation	(13)	(4)
Fair Value	2,953	2,965
Federal government and agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	411	498
Allowance for Credit Loss	0	0
Unrealized Appreciation	223	235
Unrealized Depreciation	0	0
Fair Value	634	733
State and local government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	628	729
Allowance for Credit Loss	0	0
Unrealized Appreciation	85	81
Unrealized Depreciation	0	0
Fair Value	713	810
Foreign government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,091	2,027
Allowance for Credit Loss	0	0
Unrealized Appreciation	317	230
Unrealized Depreciation	(6)	(1)
Fair Value	2,402	2,256
Corporate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	18,629	18,149
Allowance for Credit Loss	(31)	0
Unrealized Appreciation	1,890	1,299
Unrealized Depreciation	(79)	(28)
Fair Value	20,409	19,420
Mortgage and other asset-backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	514	506
Allowance for Credit Loss	(9)	0
Unrealized Appreciation	32	31
Unrealized Depreciation	(22)	(1)
Fair Value	$ 515	$ 536