Investments - Gross Unrealized Appreciation (Depreciation) on Debt Securities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 21,675	$ 21,909
Unrealized Appreciation	1,386	1,876
Unrealized Depreciation	(488)	(30)
Fair Value	22,573	23,755
Run-Off Settlement Annuity Business
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,189	2,229
Unrealized Appreciation	627	740
Unrealized Depreciation	(45)	(4)
Fair Value	2,771	2,965
Federal government and agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	411	498
Unrealized Appreciation	216	235
Unrealized Depreciation	0	0
Fair Value	627	733
State and local government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	701	729
Unrealized Appreciation	76	81
Unrealized Depreciation	0	0
Fair Value	777	810
Foreign government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,930	2,027
Unrealized Appreciation	255	230
Unrealized Depreciation	(7)	(1)
Fair Value	2,178	2,256
Corporate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	18,138	18,149
Unrealized Appreciation	823	1,299
Unrealized Depreciation	(458)	(28)
Fair Value	18,503	19,420
Corporate, with recorded allowance
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	145
Fair Value	90
Allowance for credit losses on available-for-sale debt securities	55
Mortgage and other asset-backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	495	506
Unrealized Appreciation	16	31
Unrealized Depreciation	(23)	(1)
Fair Value	$ 488	$ 536