Income Taxes - Reconciliation of Uncertain Tax Positions (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits
Unrecognized tax positions, beginning balance	$ 389.1	$ 199.8	$ 203.4
Additions for tax positions related to the current year	79.9	86.3	21.9
Additions for tax positions of prior years	88.9	120.2	12.4
Reductions for tax positions of prior years	(12.8)	(4.1)	(27.6)
Settlements with taxing authorities	(2.0)	(2.2)	(8.3)
Lapse of statute of limitations	(48.5)	(10.9)	(2.0)
Unrecognized tax positions, ending balance	$ 494.6	$ 389.1	$ 199.8