Investments - Gross Unrealized Appreciation (Depreciation) on Fixed Maturities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 20,639	$ 19,942
Unrealized Appreciation	1,231	1,196
Unrealized (Depreciation)	(136)	(177)
Total Fair Value	21,734	20,961
Run-off Settlement Annuity Business [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized Appreciation	555	539
Unrealized (Depreciation)	(12)	(15)
Total Fair Value	2,700	2,700
Federal government and agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	667	658
Unrealized Appreciation	233	223
Unrealized (Depreciation)	(3)	(4)
Total Fair Value	897	877
State and local government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,324	1,342
Unrealized Appreciation	100	99
Unrealized (Depreciation)	(5)	(6)
Total Fair Value	1,419	1,435
Foreign government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,206	1,998
Unrealized Appreciation	122	129
Unrealized (Depreciation)	(16)	(14)
Total Fair Value	2,312	2,113
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,992	15,483
Unrealized Appreciation	744	716
Unrealized (Depreciation)	(109)	(149)
Total Fair Value	16,627	16,050
Mortgage and other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	450	461
Unrealized Appreciation	32	29
Unrealized (Depreciation)	(3)	(4)
Total Fair Value	$ 479	$ 486