Long-Term Incentive Employee Compensation Summary of Stock Options by Exercise Price (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding Number	1.4	1.7	1.9	2.7
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	7 years 9 months 18 days
Options Outstanding Aggregate Intrinsic Value	$ 13.1
Options Exercisable Number	0.8	1.1	1.1
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	6 years 4 months 24 days
Options Exercisable Aggregate Intrinsic Value	$ 11.1
$19.79 Exercise Price
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding Number	0.1
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	4 years 2 months 12 days
Options Outstanding Aggregate Intrinsic Value	$ 0.6
Options Exercisable Number	0.1
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	4 years 2 months 12 days
Options Exercisable Aggregate Intrinsic Value	$ 0.6
$20.28 Exercise Price
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding Number	0.2
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	5 years 10 months 24 days
Options Outstanding Aggregate Intrinsic Value	$ 3.7
Options Exercisable Number	0.2
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	5 years 10 months 24 days
Options Exercisable Aggregate Intrinsic Value	$ 3.7
$21.53 Exercise Price
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding Number	0.1
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	5 years 2 months 12 days
Options Outstanding Aggregate Intrinsic Value	$ 0.7
Options Exercisable Number	0.1
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	5 years 2 months 12 days
Options Exercisable Aggregate Intrinsic Value	$ 0.7
$22.80 Exercise Price
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding Number	0.2
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	6 years 2 months 12 days
Options Outstanding Aggregate Intrinsic Value	$ 3.6
Options Exercisable Number	0.2
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	6 years 2 months 12 days
Options Exercisable Aggregate Intrinsic Value	$ 3.6
$26.76 Exercise Price
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding Number	0.2
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	7 years 2 months 12 days
Options Outstanding Aggregate Intrinsic Value	$ 2.5
Options Exercisable Number	0.2
Options Exercisable Weighted-Average Remaining Contractual Life (In Years)	7 years 2 months 12 days
Options Exercisable Aggregate Intrinsic Value	$ 2.5
$33.01 Exercise Price
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding Number	0.3
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	10 years 1 month 6 days
Options Outstanding Aggregate Intrinsic Value	$ 2.0
Options Exercisable Number	0.0
$41.52 Exercise Price
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding Number	0.2
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	9 years 2 months 12 days
Options Outstanding Aggregate Intrinsic Value	$ 0.0
Options Exercisable Number	0.0
$43.52 Exercise Price
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding Number	0.1
Options Outstanding Weighted-Average Remaining Contractual Life (In Years)	8 years 2 months 12 days
Options Outstanding Aggregate Intrinsic Value	$ 0.0
Options Exercisable Number	0.0