Long-Term Incentive Employee Compensation Summary of Stock Options by Exercise Price (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options Outstanding Number	0.3	0.7	0.9	1.4
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	4 years 3 months 18 days
Options Outstanding Aggregate Intrinsic Value	$ 11.6
Options Exercisable Number	0.3	0.5	0.5
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	4 years 3 months
Options Exercisable Aggregate Intrinsic Value	$ 11.6
$19.97 - $26.76
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options Outstanding Number	0.1
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	2 years 3 months 18 days
Options Outstanding Aggregate Intrinsic Value	$ 5.0
Options Exercisable Number	0.1
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	2 years 3 months
Options Exercisable Aggregate Intrinsic Value	$ 5.0
$33.01
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options Outstanding Number	0.1
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	6 years 1 month 6 days
Options Outstanding Aggregate Intrinsic Value	$ 2.9
Options Exercisable Number	0.1
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	6 years 1 month
Options Exercisable Aggregate Intrinsic Value	$ 2.9
$41.52 - $43.52
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options Outstanding Number	0.1
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	4 years 10 months 24 days
Options Outstanding Aggregate Intrinsic Value	$ 3.7
Options Exercisable Number	0.1
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	4 years 10 months 15 days
Options Exercisable Aggregate Intrinsic Value	$ 3.7