Investments (Credit Loss Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance, beginning of period	$ 179	$ 270	$ 215	$ 277
Additions:
Additional impairments — credit loss OTTI on securities previously impaired	0	6	0	8
Reductions:
Sales (maturities, pay downs or prepayments) of securities previously impaired as credit loss OTTI	(6)	(18)	(42)	(27)
Balance, end of period	$ 173	$ 258	$ 173	$ 258