Earnings Per Share Computation (Detail) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net (loss) income	$ (119,400,000)	$ (161,600,000)	$ 29,000,000	$ (70,900,000)
Less: Income allocated to participating securities	0	0	400,000	0
Net (loss) income available to common shareholders	$ (119,400,000)	$ (161,600,000)	$ 28,600,000	$ (70,900,000)
Weighted average common shares outstanding	75.1	79.8	76.0	80.6
Dilutive common share equivalents from share-based compensation plans	0	0	1.5	0
Weighted average common and common equivalent shares outstanding, assuming dilution	75.1	79.8	77.5	80.6