Net Income per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reconciliation of Net (Loss) Income and Weighted-Average Common Shares Outstanding:
Net income (loss)	$ 13.8	$ (48.2)	$ (4.5)	$ (61.9)
Basic weighted-average number of shares outstanding (in shares)	171.5	168.7	170.9	168.3
Effect of dilutive securities
Share based awards (in shares)	0.1	0	0	0
Prepaid common stock purchase contracts (shares)	44.9	0	0	0
Diluted weighted-average number of shares outstanding (in shares)	216.5	168.7	170.9	168.3
Net income (loss) per share
Basic (in dollars per share)	$ 0.08	$ (0.29)	$ (0.03)	$ (0.37)
Diluted (in dollars per share)	$ 0.06	$ (0.29)	$ (0.03)	$ (0.37)
Stock Options
Antidilutive securities excluded from computation of earnings per share
Shares excluded from calculation of diluted earnings per share (in shares)	1.9	2.5	2.0
Performance Share Units
Antidilutive securities excluded from computation of earnings per share
Shares excluded from calculation of diluted earnings per share (in shares)			1.5	0.9
Restricted Stock Units
Antidilutive securities excluded from computation of earnings per share
Shares excluded from calculation of diluted earnings per share (in shares)	1.2		1.2
Tangible Equity Units
Antidilutive securities excluded from computation of earnings per share
Shares excluded from calculation of diluted earnings per share (in shares)			44.9