Investments - Gross Unrealized Appreciation (Depreciation) on Fixed Maturities (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 21,222	$ 19,942
Unrealized Appreciation	1,380	1,196
Unrealized (Depreciation)	(89)	(177)
Total Fair Value	22,513	20,961
Run-off Settlement Annuity Business [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized Appreciation	630	539
Unrealized (Depreciation)	(3)	(15)
Total Fair Value	2,800	2,700
Federal government and agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	663	658
Unrealized Appreciation	240	223
Unrealized (Depreciation)	(3)	(4)
Total Fair Value	900	877
State and local government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,277	1,342
Unrealized Appreciation	106	99
Unrealized (Depreciation)	(2)	(6)
Total Fair Value	1,381	1,435
Foreign government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,202	1,998
Unrealized Appreciation	125	129
Unrealized (Depreciation)	(14)	(14)
Total Fair Value	2,313	2,113
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,627	15,483
Unrealized Appreciation	877	716
Unrealized (Depreciation)	(68)	(149)
Total Fair Value	17,436	16,050
Mortgage and other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	453	461
Unrealized Appreciation	32	29
Unrealized (Depreciation)	(2)	(4)
Total Fair Value	$ 483	$ 486