Earnings Per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Antidilutive securities excluded (in shares)			400,000	1,900,000
Numerator:
Net income	$ 143	$ 73	$ 247	$ 34
Subordinated convertible debt interest	0	1	0	0
Net income available to common stockholders	$ 143	$ 74	$ 247	$ 34
Denominator:
Denominator for basic earnings per share—weighted-average common shares (in shares)	93,244,000	92,539,000	93,483,000	79,681,000
Denominator for diluted earnings per share—adjusted weighted-average common shares (in shares)	105,548,000	105,273,000	106,270,000	91,500,000
Basic earnings per share (in dollars per share)	$ 1.53	$ 0.78	$ 2.65	$ 0.42
Diluted earnings per share (in dollars per share)	$ 1.35	$ 0.70	$ 2.33	$ 0.37
Employee stock options and warrants [Member]
Denominator:
Incremental common shares attributable to share-based payment arrangements (in shares)	463,000	707,000	527,000	759,000
Convertible subordinated notes—1 7/8 percent [Member]
Denominator:
Convertible subordinated notes (in shares)	0	208,000	0	0
Convertible subordinated notes—4 percent [Member]
Denominator:
Convertible subordinated notes (in shares)	11,407,000	10,031,000	11,744,000	10,543,000
Subordinated convertibe debentures [Member]
Denominator:
Convertible subordinated notes (in shares)	0	1,341,000	0	0
Restricted stock units [Member]
Denominator:
Incremental common shares attributable to share-based payment arrangements (in shares)	434,000	447,000	516,000	517,000
Convertible subordinated notes—1 7/8 percent [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stated interest rate	1.875%		1.875%
Convertible subordinated notes—4 percent [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Stated interest rate	4.00%		4.00%