Investments - Gross Unrealized Appreciation (Depreciation) on Fixed Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 22,550	$ 21,867
Unrealized Appreciation	852	1,371
Unrealized (Depreciation)	(474)	(100)
Total Fair Value	22,928	23,138
Run-off Settlement Annuity Business [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,264	2,200
Unrealized Appreciation	479	681
Unrealized (Depreciation)	(40)	(2)
Total Fair Value	2,703	2,879
Fixed maturities [Member]
Schedule of Available-for-sale Securities [Line Items]
Commitments to make additional investments	106
Federal government and agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	507	541
Unrealized Appreciation	204	239
Unrealized (Depreciation)	(1)	(1)
Total Fair Value	710	779
State and local government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	920	1,196
Unrealized Appreciation	66	93
Unrealized (Depreciation)	(1)	(2)
Total Fair Value	985	1,287
Foreign government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,214	2,360
Unrealized Appreciation	155	142
Unrealized (Depreciation)	(7)	(15)
Total Fair Value	2,362	2,487
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,403	17,301
Unrealized Appreciation	411	868
Unrealized (Depreciation)	(453)	(81)
Total Fair Value	18,361	18,088
Mortgage and other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	506	469
Unrealized Appreciation	16	29
Unrealized (Depreciation)	(12)	(1)
Total Fair Value	$ 510	$ 497