Stockholders' Equity - Changes in Equity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 838	$ 1,109	$ 831	$ 1,180
Total comprehensive income	37	66	152	142
Common stock dividends	(8)	(9)	(26)	(27)
Distributions to noncontrolling interests	(2)	(2)	(16)	(8)
Common stock share repurchases	0	(119)	(81)	(245)
Derecognition of noncontrolling interests			0	(5)
Stock compensation	5	7	11	17
Stock withheld for employee taxes	0	(1)	(1)	(3)
Ending Balance	870	1,051	870	1,051
Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	743	1,006	728	1,080
Total comprehensive income	33	66	142	128
Common stock dividends	(8)	(9)	(26)	(27)
Common stock share repurchases		(119)	(81)	(245)
Stock compensation	5	7	11	17
Stock withheld for employee taxes		(1)	(1)	(3)
Ending Balance	773	950	773	950
Attributable to Non-Controlling Interests [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	95	103	103	100
Total comprehensive income	4		10	14
Distributions to noncontrolling interests	(2)	(2)	(16)	(8)
Derecognition of noncontrolling interests				(5)
Ending Balance	$ 97	$ 101	$ 97	$ 101