Share-Based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	$ 6.1		$ 7.1	$ 9.9	$ 11.1
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	0.2		0.4	0.5	0.8
Intrinsic value of options exercised			0.4	1.0	0.4
Excess tax benefits shown as financing cash inflows	0		0.1	0.3	0.1
Unrecognized share-based compensation cost	1.1			1.1
Unrecognized compensation expense, weighted-average period of recognition				1 year 6 months
Restricted stock units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	4.9		6.0	7.8	9.2
Excess tax benefits shown as financing cash inflows	0.3		0.9	2.5	2.2
Unrecognized share-based compensation cost	18.2			18.2
Unrecognized compensation expense, weighted-average period of recognition				2 years 4 months 24 days
Equity instruments other than options expected to vest, Shares	1,900,000			1,900,000
Equity instruments other than options expected to vest, weighted-average grant date fair value	$ 12.55			$ 12.55
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation	1.0		0.7	1.6	1.1
Unrecognized share-based compensation cost	$ 7.2			$ 7.2
Unrecognized compensation expense, weighted-average period of recognition				2 years 1 month 6 days
Performance share unit awards granted to certain executive officers				319,000
Equity instruments other than options, payout range, minimum				154,500
Equity instruments other than options, payout range, maximum				319,000	485,000	233,000
Compensation expense achieved target, percentage		52.00%
Compensation expense achieved target, shares		121,431