Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Contingency [Line Items]
Corporate income tax rate			21.00%	21.00%	35.00%
Provisional Income tax expense	$ 6.7	$ 81.8		$ 0.0	$ 81.8
Income tax expense related to one time mandatory tax		83.5
Income tax expense due to tax rate reform		$ 1.7
Total taxes paid			$ 116.6	$ 116.4	$ 131.1
Cash and cash equivalents and marketable securities were held by foreign subsidiaries			548.6
Unrecognized tax benefits that would affect the effective tax rate, if recognized			0.8
Anticipated decrease in unrecognized tax benefits			$ 0.0
State and local | Earliest Tax Year
Income Tax Contingency [Line Items]
Income tax examinations, years under examination			2002
State and local | Latest Tax Year
Income Tax Contingency [Line Items]
Income tax examinations, years under examination			2019
Non-U.S. | Earliest Tax Year
Income Tax Contingency [Line Items]
Income tax examinations, years under examination			2013
Non-U.S. | Latest Tax Year
Income Tax Contingency [Line Items]
Income tax examinations, years under examination			2019
U.S. federal | Earliest Tax Year
Income Tax Contingency [Line Items]
Income tax examinations, years under examination			2016
U.S. federal | Latest Tax Year
Income Tax Contingency [Line Items]
Income tax examinations, years under examination			2019
Discontinued Operations
Income Tax Contingency [Line Items]
Additional income tax accrual			$ 20.8