Source of income Before Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Loss From Operations Before Provision Benefit For Income Taxes [Line Items]
United States	$ 1,098.5	$ 37.2	$ 913.9
International	688.3	520.8	465.7
Income before provision for income taxes	$ 1,786.8	$ 558.0	$ 1,379.6