Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 22, 2017
Income Tax Contingency [Line Items]
Effective tax rate	14.60%	23.40%
Overall increase (decrease) in unrecognized tax benefits (UTPs)	$ 101.8
Excess Tax Benefit from Share Based Compensation	31.0	$ 19.0
Estimated Repatriation Tax Liability Resulting from Tax Reform Legislation				$ 247.3
U.S. Statutory Tax Rate			35.00%
Net of federal tax benefit [Member]
Income Tax Contingency [Line Items]
Overall increase (decrease) in unrecognized tax benefits (UTPs)	$ 109.6
Tax Reform [Member]
Income Tax Contingency [Line Items]
U.S. Statutory Tax Rate			21.00%