Condensed Consolidated Statements of Equity (Unaudited) (USD $) In Millions, except Share data	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]	Total
Balance at Dec. 31, 2011	$ 586	$ 1,989	$ 967	$ (217)	$ (7)	$ 21	$ 3,339
Balance (in Shares) at Dec. 31, 2011	117,000,000
Net income			130			9	139
Other comprehensive loss				(1)			(1)
Dividends on common stock			(42)				(42)
Distributions to noncontrolling interest						(14)	(14)
Stock issued, dividend reinvestment plan	1	3			(1)		3
Stock issued, dividend reinvestment plan (in Shares)	200,000
Stock-based compensation expense (net of tax)		2					2
Balance at Mar. 31, 2012	587	1,994	1,055	(218)	(8)	16	3,426
Balance (in Shares) at Mar. 31, 2012	117,200,000						117,282,844
Balance at Dec. 31, 2012	590	2,014	1,035	(218)	(8)	22	3,435
Balance (in Shares) at Dec. 31, 2012	117,900,000						117,855,075
Net income			154			10	164
Other comprehensive loss				7			7	[1]
Dividends on common stock			(55)				(55)
Distributions to noncontrolling interest						(17)	(17)
Stock granted, share-based compensation, net of forfeitures		(6)					(6)
Stock issued, dividend reinvestment plan	1	2					3
Stock issued, share-based compensation, net of forfeitures	1	6					7
Stock issued, share-based compensation, net of forfeitures (in Shares)	200,000
Stock-based compensation expense (net of tax)		3					3
Balance at Mar. 31, 2013	$ 592	$ 2,019	$ 1,134	$ (211)	$ (8)	$ 15	$ 3,541
Balance (in Shares) at Mar. 31, 2013	118,100,000						118,123,770

[1] All amounts are net of income taxes. Amounts in parentheses indicate debits to Accumulated Other Comprehensive Loss.