Investments (Credit Loss Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at January 1,	$ 0	$ 28
Reductions:
Sales (maturities, pay downs or prepayments) of securities previously impaired as credit loss OTTI	0	(18)
Balance at March 31,	$ 0	$ 10