Investments (Investment Income (Loss), Net) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Gains on sales and exchanges of investments, net	$ 46	$ 12	$ 192
Investment impairment losses	(34)	(59)	(50)
Unrealized gains (losses) on securities underlying prepaid forward sale agreements	0	42	66
Mark to market adjustments on derivative component of prepaid forward sale agreements and indexed debt instruments	(4)	(42)	(56)
Interest and dividend income	123	115	116
Other, net	82	13	28
Investment income (loss), net	$ 213	$ 81	$ 296