Share-Based Compensation - Additional Information (Detail) (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	Sep. 30, 2011
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 4.5	$ 3.8	$ 15.6	$ 18.6
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	0.3	0.6	1.1	2.4
Stock options granted			0	1,221,000
Grant date fair market value of options granted				$ 2.96
Intrinsic value of options exercised	0.3	0	0.7	1.2
Unrecognized share-based compensation cost	2.1		2.1
Options that are expected to vest	1,000,000		1,000,000
Weighted average fair market value of nonvested options	$ 3.28		$ 3.28
Unrecognized compensation expense, weighted-average period of recognition			2 years
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	3.6	3.8	12.8	15.8
Unrecognized share-based compensation cost	17.6		17.6
Unrecognized compensation expense, weighted-average period of recognition			2 years 3 months 18 days
Equity instruments other than options expected to vest, Shares	2,400,000		2,400,000
Equity instruments other than options expected to vest, weighted-average grant date fair value	$ 11.97		$ 11.97
Granted, Shares			1,402,000
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	0.6	(0.6)	1.7	0.4
Unrecognized share-based compensation cost	$ 4.3		$ 4.3
Unrecognized compensation expense, weighted-average period of recognition			2 years
Granted, Shares			485,000
Equity instruments other than options, payout range, minimum			242,500		117,500
Equity instruments other than options, payout range, maximum			485,000	233,000
Equity instruments other than options, percentage of expected payout					50.00%