Investments (Credit Loss Rollforward) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at January 1,	$ 277	$ 357
Additions:
Initial impairments — credit loss OTTI on securities not previously impaired	1	20
Additional impairments — credit loss OTTI on securities previously impaired	23	26
Reductions:
Sales (maturities, pay downs or prepayments) of securities previously impaired as credit loss OTTI	(85)	(124)
Securities impaired to net present value of expected future cash flows	(1)	0
Increase in cash flows — accretion of previous credit loss OTTI	0	(2)
Balance at December 31,	$ 215	$ 277