Income Taxes - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	[1]	19.30%	20.00%	20.30%
Gross unrecognized tax benefits		$ 36.6	$ 71.1	$ 45.6	$ 40.3
Amount of tax benefits that, if recognized, would impact the effective tax rate		34.9
Gross increases for tax positions in prior periods		5.3	27.4	$ 4.7
Payment of penalties		2.3	2.4
Payment of interest expense		9.4	11.0
Tax loss carryforwards		4,052.9
Deferred tax assets, valuation allowance		792.4	$ 380.8
Non-U.S. tax losses available for carry forward		3,961.0
Deferred Tax Assets, Operating Loss Carryforwards, Domestic		2,253.0
State tax losses available for carry forward		91.9
Minimum
Income Taxes [Line Items]
Possible amount of decrease during the next twelve months primarily as a result of the resolution of federal, state and foreign examinations and the expiration of various statutes of limitations		0.0
Maximum
Income Taxes [Line Items]
Possible amount of decrease during the next twelve months primarily as a result of the resolution of federal, state and foreign examinations and the expiration of various statutes of limitations		$ 16.9
Operating loss carryforwards expiration year		2037
Foreign Country
Income Taxes [Line Items]
Deferred tax assets, valuation allowance		$ 762.2

[1] The statutory rate for 2017, 2016 and 2015 reflects the U.K. statutory rate of 19.3%, 20.0% and 20.3%, respectively.