Investments (Investment Income (Loss), Net) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Investments [Abstract]
Gains (losses) on sales and exchanges of investments, net	$ 0	$ 13	$ (1)	$ 15
Investment impairment losses	(2)	(1)	(6)	(21)
Interest and dividend income	32	31	65	60
Other, net	34	15	65	34
Investment income (loss), net	$ 64	$ 58	$ 123	$ 88