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			164			10	174
Other comprehensive loss				10			10
Dividends on common stock			(96)				(96)
Distributions to noncontrolling interest						(14)	(14)
Stock issued, dividend reinvestment plan	3	9			(1)		11
Stock issued, dividend reinvestment plan (in Shares)	500,000
Stock-based compensation expense (net of tax)		5					5
Balance at Jun. 30, 2012	589	2,003	1,035	(207)	(8)	17	3,429
Balance (in Shares) at Jun. 30, 2012	117,500,000						117,505,440
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			203			11	214
Other comprehensive loss				9			9
Dividends on common stock			(111)				(111)
Distributions to noncontrolling interest						(17)	(17)
Stock granted, share-based compensation, net of forfeitures		(6)					(6)
Stock issued, dividend reinvestment plan	1	5					6
Stock issued, dividend reinvestment plan (in Shares)	100,000
Stock issued, share-based compensation, net of forfeitures	3	18					21
Stock issued, share-based compensation, net of forfeitures (in Shares)	600,000
Stock-based compensation expense (net of tax)		4					4
Balance at Jun. 30, 2013	$ 594	$ 2,035	$ 1,127	$ (209)	$ (8)	$ 16	$ 3,555
Balance (in Shares) at Jun. 30, 2013	118,600,000						118,560,687