Investments - Gross Unrealized Appreciation (Depreciation) on Fixed Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 19,942	$ 18,456
Unrealized Appreciation	1,196	1,218
Unrealized (Depreciation)	(177)	(219)
Total Fair Value	20,961	19,455
Commitments to purchase fixed maturities	26
Run-off Settlement Annuity Business [Member]
Schedule of Available-for-sale Securities [Line Items]
Unrealized Appreciation	539	521
Unrealized (Depreciation)	(15)	(38)
Total Fair Value	2,700	2,700
Federal government and agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	658	528
Unrealized Appreciation	223	251
Unrealized (Depreciation)	(4)	0
Total Fair Value	877	779
State and local government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,342	1,496
Unrealized Appreciation	99	147
Unrealized (Depreciation)	(6)	(2)
Total Fair Value	1,435	1,641
Foreign government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,998	1,870
Unrealized Appreciation	129	147
Unrealized (Depreciation)	(14)	(3)
Total Fair Value	2,113	2,014
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,483	14,022
Unrealized Appreciation	716	632
Unrealized (Depreciation)	(149)	(206)
Total Fair Value	16,050	14,448
Mortgage and other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	461	540
Unrealized Appreciation	29	41
Unrealized (Depreciation)	(4)	(8)
Total Fair Value	$ 486	$ 573