Equity (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs			$ 2,000,000
Proceeds from Issuance of Common Stock	314,000,000		47,000,000	0
Common Stock, Shares, Outstanding beginning of period			75,556,272
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			1,730,000,000
Net Income (Loss) Attributable to Parent	(22,000,000)	26,000,000		75,000,000
Net Income (Loss) Attributable to Noncontrolling Interest	0	0		0
Common Stock, Shares, Outstanding end of period	77,362,458		77,362,458
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,762,000,000		1,762,000,000
Share Price	$ 29.50		$ 29.50
Sale of Stock, Price Per Share	$ 28.54		$ 28.54
Common Stock, Discount on Shares	0.96		0.96
stock offering	11,100,000
Option Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	26,000,000		26,000,000
underwriters discount	11,000,000		11,000,000
Net share settlement	844,757		844,757
Common Stock [Member]
Stock Issued During Period, Shares, New Issues			1,665,000
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures			141,186	164,325
Common Stock, Shares, Outstanding beginning of period			75,556,272	75,362,956
Common Stock, Shares, Outstanding end of period	77,362,458	75,527,281	77,362,458	75,527,281
Common Stock Including Additional Paid in Capital [Member]
Proceeds from Issuance of Common Stock			47,000,000
Share-based Compensation			1,000,000	1,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			841,000,000	836,000,000
Dividends, Common Stock			0	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	889,000,000	837,000,000	889,000,000	837,000,000
Accumulated Other Comprehensive Income (Loss) [Member]
Share-based Compensation			0	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			(6,000,000)	(6,000,000)
Dividends, Common Stock			0	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(6,000,000)	(6,000,000)	(6,000,000)	(6,000,000)
Retained Earnings [Member]
Share-based Compensation			0	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			893,000,000	833,000,000
Dividends, Common Stock			(42,000,000)	(41,000,000)
Net Income (Loss) Attributable to Parent			27,000,000	75,000,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	878,000,000	867,000,000	878,000,000	867,000,000
Noncontrolling Interest [Member]
Share-based Compensation			0	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			2,000,000	3,000,000
Dividends, Common Stock			0	0
Net Income (Loss) Attributable to Noncontrolling Interest			(1,000,000)	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 1,000,000	$ 3,000,000	$ 1,000,000	$ 3,000,000