Investments - Write Downs and Sales (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Realized Gains (Losses) on Investments [Line Items]
Total		$ (7)	$ (15)	$ (43)	$ (26)
Sales Information For Available For Sale Fixed Maturities Equity Securities [Abstract]
Proceeds from sales		351	784	712	1,177
Gross gains on sales		22	24	34	51
Gross losses on sales		1	2	6	4
Debt Securities [Member]
Realized Gains (Losses) on Investments [Line Items]
Credit-related		(1)	(1)	(19)	(1)
Non-credit related	[1]	(2)	(9)	(11)	(14)
Total		(3)	(10)	(30)	(15)
Other [Member]
Realized Gains (Losses) on Investments [Line Items]
Total	[2]	$ (4)	$ (5)	$ (13)	$ (11)

[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 their amortized cost basis.

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