Income Tax Provision (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Effective income tax rates	0.40%	(0.80%)	11.00%	(0.10%)
Excess tax benefit	$ 11.6	$ 9.3	$ 18.6	$ 30.0
Effective income tax rate excluding excess tax benefit	28.90%	23.30%	27.60%	25.80%
Income tax payments			$ 18.1	$ 6.8

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to expense for award under share-based payment arrangement. Excludes expense determined to be nondeductible upon grant or after for award under share-based payment arrangement.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income.

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