Investments - Write Downs and Sales (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Realized Gains (Losses) on Investments [Line Items]
Total		$ (1)	$ (59)	$ (44)	$ (85)
Sales Information For Available For Sale Fixed Maturities Equity Securities [Abstract]
Proceeds from sales		300	275	1,012	1,452
Gross gains on sales		9	31	43	82
Gross losses on sales		0	3	6	7
Debt Securities [Member]
Realized Gains (Losses) on Investments [Line Items]
Credit-related		0	(3)	(19)	(4)
Non-credit related	[1]	(1)	(55)	(12)	(69)
Total		(1)	(58)	(31)	(73)
Other [Member]
Realized Gains (Losses) on Investments [Line Items]
Total	[2]	$ 0	$ (1)	$ (13)	$ (12)

[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.