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
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	$ 29.9	$ 48.5	$ 62.9
Associated tax benefits recognized	4.9	11.8	19.7
2018 Three-year PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	2.7	0.0	0.0
2017 Three-year PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	3.7	9.8	0.0
2017 COO and Chief Executive Officer-Designate 2017 New Hire Equity Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	0.2	0.1	0.0
2016 Three-year PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	(3.0)	2.0	6.3
2016 President & CEO Inducement Award
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	0.0	0.5	0.5
2015 Three-year PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	0.0	(0.8)	3.5
2014 Special PSU Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	0.0	3.2	8.8
Share-based compensation expense settled in cash		1.0
2014 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	4.9
2012 President & COO Four-year Incentive Compensation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	0.0	0.0	0.2
SLO Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total share-based incentive compensation expense	1.6	1.1	2.5
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	$ 24.7	$ 32.6	$ 36.2

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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