Investments (Credit Loss Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance, beginning of period	$ 258	$ 280	$ 277	$ 357
Additions:
Initial impairments — credit loss OTTI on securities not previously impaired	1	0	1	2
Additional impairments — credit loss OTTI on securities previously impaired	10	1	18	14
Reductions:
Sales (maturities, pay downs or prepayments) of securities previously impaired as credit loss OTTI	(17)	(22)	(43)	(113)
Securities impaired to net present value of expected future cash flows	0	0	(1)	0
Increase in cash flows — accretion of previous credit loss OTTI	0	(1)	0	(2)
Balance, end of period	$ 252	$ 258	$ 252	$ 258