Investments - Write Downs and Sales (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Realized Gains (Losses) on Investments [Line Items]
Total		$ (58)	$ (140)	$ (52)
Realized Investment Results Not Reflected In Revenues Table Details [Abstract]
Separate accounts		16	117	376
Investment gains required to adjust future policy benefits for the run-off settlement annuity business		63	114	86
Sales Information For Available For Sale Fixed Maturities Equity Securities [Abstract]
Proceeds from sales		1,544	1,555	1,769
Gross gains on sales		83	85	62
Gross losses on sales		7	13	6
Fixed Maturities [Member]
Realized Gains (Losses) on Investments [Line Items]
Credit-related		(19)	(11)	0
Non-credit related	[1]	(16)	(101)	(36)
Total		(35)	(112)	(36)
Other [Member]
Realized Gains (Losses) on Investments [Line Items]
Total	[2]	$ (23)	$ (28)	$ (16)

[1] These write-downs pertain to other-than-temporary declines in fair values due to increases in market yields (widening of credit spreads), particularly within the energy sector, for certain below investment grade fixed maturities with an increased probability of sales activity prior to recovery of amortized cost basis.

[2] Other asset write-downs include other-than-temporary declines in the fair values of equity securities, increases in valuation reserves on commercial mortgage loans, and asset write-downs related to security partnerships and real estate investments.