Consolidated Statements of Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Shares [Member]	Noncontrolling Interest [Member]
Balance at Dec. 31, 2012	$ 3,391	$ 590	$ 2,015	$ 990	$ (218)	$ (8)	$ 22
Balance (in shares) at Dec. 31, 2012		117,900,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	313			295			18
Other comprehensive income (loss)	82				82
Dividends on common stock	(222)			(222)
Distribution to noncontrolling interest	(17)						(17)
Contribution from noncontrolling interest	22						22
Stock granted, share-based compensation, net of forfeitures	(6)		(6)
Stock issued, dividend reinvestment plan	11	$ 1	10
Stock issued, dividend reinvestment plan (in shares)		300,000
Stock issued, share-based compensation, net of forfeitures	28	$ 4	24
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	3,613	$ 595	2,054	1,063	(136)	(8)	45
Balance (in shares) at Dec. 31, 2013		118,900,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	500			482			18
Other comprehensive income (loss)	(72)				(70)		(2)
Dividends on common stock	(233)			(233)
Distribution to noncontrolling interest	(17)						(17)
Stock granted, share-based compensation, net of forfeitures	(11)		(11)
Stock issued, dividend reinvestment plan	12	$ 1	11
Stock issued, dividend reinvestment plan (in shares)		200,000
Stock issued, share-based compensation, net of forfeitures	22	$ 3	19
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	$ 3,828	$ 599	2,087	1,312	(206)	(8)	44
Balance (in shares) at Dec. 31, 2014	119,647,149	119,600,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 373			353			20
Other comprehensive income (loss)	20				20		0
Dividends on common stock	(244)			(244)
Distribution to noncontrolling interest	(18)						(18)
Stock granted, share-based compensation, net of forfeitures	(14)		(14)
Stock issued, dividend reinvestment plan	12	$ 1	11
Stock issued, dividend reinvestment plan (in shares)		300,000
Stock issued, share-based compensation, net of forfeitures	16	$ 3	13
Stock issued, share-based compensation, net of forfeitures (in shares)		500,000
Stock-based compensation expense, net of tax	2		2
Balance at Dec. 31, 2015	$ 3,975	$ 603	$ 2,099	$ 1,421	$ (186)	$ (8)	$ 46
Balance (in shares) at Dec. 31, 2015	120,376,721	120,400,000