Condensed Consolidated Statements of Equity (Unaudited) (USD $) In Millions	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, 2010	$ 391	$ 631	$ 943	$ (150)	$ (2)	$ 23	$ 1,836
Balance (in Shares) at Dec. 31, 2010	78.0
Net income			139			10	149
Other comprehensive loss				(1)			(1)
Dividends on common stock			(105)				(105)
Distributions to noncontrolling interest						(16)	(16)
Stock granted, share-based compensation, net of forfeitures		(5)					(5)
Stock issued, dividend reinvestment plan	1	6					7
Stock issued, dividend reinvestment plan (in Shares)	0.2
Stock issued, share-based compensation, net of forfeitures	2	12			(2)		12
Stock issued, share-based compensation, net of forfeitures (in Shares)	0.3
Purchase of treasury shares					(2)		(2)
Stock-based compensation expense (net of tax)		6					6
Balance at Sep. 30, 2011	394	650	977	(151)	(6)	17	1,881
Balance (in Shares) at Sep. 30, 2011	78.5						78,539,528.0
Balance at Dec. 31, 2011	586	1,989	967	(217)	(7)	21	3,339
Balance (in Shares) at Dec. 31, 2011	117.0						117,044,803.0
Net income			173			10	183
Other comprehensive loss				14			14
Dividends on common stock			(150)				(150)
Distributions to noncontrolling interest						(14)	(14)
Stock granted, share-based compensation, net of forfeitures		(9)					(9)
Stock issued, dividend reinvestment plan	1	7					8
Stock issued, dividend reinvestment plan (in Shares)	0.2
Stock issued, share-based compensation, net of forfeitures	3	17			(1)		19
Stock issued, share-based compensation, net of forfeitures (in Shares)	0.5
Stock-based compensation expense (net of tax)		8					8
Balance at Sep. 30, 2012	$ 590	$ 2,012	$ 990	$ (203)	$ (8)	$ 17	$ 3,398
Balance (in Shares) at Sep. 30, 2012	117.7						117,743,809.0