Consolidated Statements of Equity (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
As of December 31, 2011 at Dec. 31, 2011	$ 586	$ 1,989	$ 933	$ (217)	$ (7)	$ 21	$ 3,305
As of December 31, 2011 (in Shares) at Dec. 31, 2011	117,000,000
Net income			260			15	275
Other comprehensive income				(1)			(1)
Dividends on common stock			(203)				(203)
Distributions to noncontrolling interest						(14)	(14)
Stock granted, share-based compensation, net of forfeitures		(10)					(10)
Stock issued, dividend reinvestment plan	1	9					10
Stock issued, dividend reinvestment plan (in Shares)	300,000
Stock issued, share-based compensation, net of forfeitures	3	19			(1)		21
Stock issued, share-based compensation, net of forfeitures (in Shares)	600,000
Stock-based compensation expense, net of tax		8					8
Balance at Dec. 31, 2012	590	2,015	990	(218)	(8)	22	3,391
Balance, shares (in Shares) at Dec. 31, 2012	117,900,000
Net income			295			18	313
Other comprehensive income				82			82
Dividends on common stock			(222)				(222)
Contribution from noncontrolling interest						22	22
Distributions to noncontrolling interest						(17)	(17)
Stock granted, share-based compensation, net of forfeitures		(6)					(6)
Stock issued, dividend reinvestment plan	1	10					11
Stock issued, dividend reinvestment plan (in Shares)	300,000
Stock issued, share-based compensation, net of forfeitures	4	24					28
Stock issued, share-based compensation, net of forfeitures (in Shares)	700,000
Stock-based compensation expense, net of tax		11					11
Balance at Dec. 31, 2013	595	2,054	1,063	(136)	(8)	45	3,613
Balance, shares (in Shares) at Dec. 31, 2013	118,900,000						118,888,876
Net income			482			18	500
Other comprehensive income				(70)		(2)	(72)
Dividends on common stock			(233)				(233)
Distributions to noncontrolling interest						(17)	(17)
Stock granted, share-based compensation, net of forfeitures		(11)					(11)
Stock issued, dividend reinvestment plan	1	11					12
Stock issued, dividend reinvestment plan (in Shares)	200,000
Stock issued, share-based compensation, net of forfeitures	3	19					22
Stock issued, share-based compensation, net of forfeitures (in Shares)	500,000
Stock-based compensation expense, net of tax		14					14
Balance at Dec. 31, 2014	$ 599	$ 2,087	$ 1,312	$ (206)	$ (8)	$ 44	$ 3,828
Balance, shares (in Shares) at Dec. 31, 2014	119,600,000						119,647,149