Stockholders' Equity - Changes in Equity (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Stockholders Equity Note [Line Items]
Beginning Balance	$ 1,948	$ 1,838
Total comprehensive income	43	130
Preferred stock dividends	(8)	(8)
Common stock dividends	(8)	(7)
Distributions to noncontrolling interests	(1)
Common stock share repurchases	(24)
Adjustments to paid-in capital for purchase of noncontrolling interests	6
Purchase of noncontrolling interests	(9)
Stock compensation	6	5
Stock withheld for employee taxes	(2)
Ending Balance	1,948	1,958
To US Parent
Stockholders Equity Note [Line Items]
Beginning Balance	1,843	1,737
Total comprehensive income	37	126
Preferred stock dividends	(8)	(8)
Common stock dividends	(8)	(7)
Common stock share repurchases	(24)
Adjustments to paid-in capital for purchase of noncontrolling interests	6
Stock compensation	6	5
Stock withheld for employee taxes	(2)
Ending Balance	1,847	1,853
Attributable to Non-Controlling Interests
Stockholders Equity Note [Line Items]
Beginning Balance	105	101
Total comprehensive income	6	4
Distributions to noncontrolling interests	(1)
Purchase of noncontrolling interests	(9)
Ending Balance	$ 101	$ 105