Investments (Investment Income (Loss), Net) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Investments [Abstract]
Gains (losses) on sales and exchanges of investments, net	$ 10	$ 24	$ 9	$ 39
Investment impairment losses	(3)	(7)	(9)	(28)
Interest and dividend income	36	31	101	91
Other, net	39	32	104	66
Investment income (loss), net	$ 82	$ 80	$ 205	$ 168