Stockholders' Equity (Deficit) - Summarizes the Company's Pre-tax Share-based Incentive Compensation Expense and Income Tax Benefit (Detail) - USD ($) $ in Millions		12 Months Ended
	May 18, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense		$ 42.3	$ 34.4	$ 29.9
Associated tax benefits recognized		7.1	5.8	4.9
2020 Three-year PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense		5.3	0.0	0.0
2019 Three-year PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense		3.5	4.3	0.0
2018 Three-year PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense		1.9	0.2	2.7
Shares issued for 2017 Three-Year PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense		0.0	0.0	3.7
PSU awards performance period	3 years
2017 COO and Chief Executive Officer-Designate New Hire Equity Awards(2)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense		0.2	0.2	0.2
2016 Three-year PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense		0.0	0.0	(3.0)
PSU awards performance period	3 years
SLO Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense		2.2	3.2	1.6
Other long-term share-based incentive compensation programs
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense		$ 29.2	$ 26.5	$ 24.7