Stockholders' Equity - Changes in Equity (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 1,426	$ 1,911	$ 1,413	$ 1,948
Total comprehensive income (loss)	(21)	111	122	190
Preferred stock dividends	(2)	(6)	(7)	(21)
Common stock dividends	(7)	(7)	(23)	(22)
Distributions to noncontrolling interests	(1)	(6)	(8)	(11)
Preferred stock redemption	0	(474)	0	(474)
Share conversion			3	0
Common stock share repurchases	(68)	(202)	(181)	(288)
Adjustments to paid-in capital for purchase of noncontrolling interests			0	6
Adjustments to other comprehensive income for purchase of noncontrolling interests			0	(3)
Purchase of noncontrolling interests			0	(9)
Repurchase of equity awards	0	(2)	0	(2)
Stock compensation	6	10	16	25
Stock withheld for employee taxes			(2)	(4)
Ending Balance	1,333	1,335	1,333	1,335
Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	1,322	1,806	1,309	1,836
Total comprehensive income (loss)	(22)	106	114	178
Preferred stock dividends	(2)	(6)	(7)	(21)
Common stock dividends	(7)	(7)	(23)	(22)
Share conversion			3
Common stock share repurchases	(68)	(202)	(181)	(288)
Adjustments to paid-in capital for purchase of noncontrolling interests				6
Adjustments to other comprehensive income for purchase of noncontrolling interests				(3)
Repurchase of equity awards		(2)		(2)
Stock compensation	6	10	16	25
Stock withheld for employee taxes			(2)	(4)
Ending Balance	1,229	1,231	1,229	1,231
Attributable to Non-Controlling Interests [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	104	105	104	112
Total comprehensive income (loss)	1	5	8	12
Distributions to noncontrolling interests	(1)	(6)	(8)	(11)
Purchase of noncontrolling interests				(9)
Ending Balance	104	104	104	104
Series B Preferred Stock [Member] | Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock redemption		$ (474)		$ (474)