Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2017
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, Percent	20.94082%		22.10%
Total gross liability for unrecognized tax benefits	$ 35.3	$ 36.6		$ 36.6
Transition tax expense		62.9
Federal Tax Reform [Member]
Income Taxes [Line Items]
Federal Statutory Income Tax Rate, Historical				35.00%
Tax Cuts and Jobs Act of 2017, Corporate Federal Tax Rate				21.00%
Provisional income tax benefit		84.8
Decrease of income tax expense related to remeasurement of certain deferred tax assets and liabilities due to lower tax rate		$ 147.7