Investments (Credit Loss Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance, beginning of period	$ 277	$ 357
Additions:
Initial impairments — credit loss OTTI on securities not previously impaired	0	2
Additional impairments — credit loss OTTI on securities previously impaired	2	11
Reductions:
Sales (maturities, pay downs or prepayments) of securities previously impaired as credit loss OTTI	(9)	(13)
Balance, end of period	$ 270	$ 357