Investments - Write Downs and Sales (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Realized Gains (Losses) on Investments [Line Items]
Total		$ (10)	$ (36)
Sales Information For Available For Sale Fixed Maturities Equity Securities [Abstract]
Proceeds from sales		414	361
Gross gains on sales		47	12
Gross losses on sales		2	5
Fixed Maturities [Member]
Realized Gains (Losses) on Investments [Line Items]
Credit-related		(5)	(18)
Non-credit related	[1]	(2)	(9)
Total		(7)	(27)
Other [Member]
Realized Gains (Losses) on Investments [Line Items]
Total	[2]	$ (3)	$ (9)

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

[2] Other asset write-downs include other-than-temporary declines in fair values of equity securities and asset write-downs related to real estate investments.