Stockholders' Equity - Changes in Equity (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 1,413	$ 1,948
Total comprehensive income	31	43
Preferred stock dividends	(3)	(8)
Common stock dividends	(7)	(8)
Distributions to noncontrolling interests	(1)	(1)
Share conversion	3	0
Common stock share repurchases	(64)	(24)
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)
Stock compensation	6	6
Stock withheld for employee taxes	(1)	(2)
Ending Balance	1,377	1,948
Attributable to Parent [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	1,309	1,836
Total comprehensive income	29	37
Preferred stock dividends	(3)	(8)
Common stock dividends	(7)	(8)
Share conversion	3
Common stock share repurchases	(64)	(24)
Adjustments to paid-in capital for purchase of noncontrolling interests		6
Adjustments to other comprehensive income for purchase of noncontrolling interests		(3)
Stock compensation	6	6
Stock withheld for employee taxes	(1)	(2)
Ending Balance	1,272	1,840
Attributable to Non-Controlling Interests [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	104	112
Total comprehensive income	2	6
Distributions to noncontrolling interests	(1)	(1)
Purchase of noncontrolling interests		(9)
Ending Balance	$ 105	$ 108