Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Taxes [Line Items]
Effective income tax rate	37.80%	26.90%
Increase/(decrease) in effective tax rate due to impact of discrete tax items	3.80%	0.30%
Tax benefit	$ 74.5	$ 52.3
Income tax expense at federal statutory rate	21.00%		35.00%
Net increase to income tax reserves for unrecognized tax benefits based on tax positions related to current and prior years	$ 2.0
Decrease of income tax reserves for unrecogonized tax benefits	1.9
Unrecognized tax benefits reserve that would impact effective tax rate if released into income	34.7
Current Tax Payable Part of Other Current Liabilities
Income Taxes [Line Items]
Unrecognized tax benefits reserve that would impact effective tax rate if released into income	7.4
Non-Current Tax Payable Part of Other Non-current Liabilities
Income Taxes [Line Items]
Unrecognized tax benefits reserve that would impact effective tax rate if released into income	27.3
GILTI and BEAT
Income Taxes [Line Items]
Tax benefit	$ 0.0