Components of Comprehensive Income, Net of Related Tax (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 629.0	$ 512.1
Other comprehensive (loss) income (OCI):
Unrealized losses on derivative contracts	(15.8)	(4.1)
Tax effect	4.2	1.6
Net current period OCI, unrealized losses on derivative contracts	(11.6)	(2.5)
Unrealized gains (losses) on marketable debt securities	6.2	(2.6)
Tax effect	(1.6)	0.6
Net current period OCI, unrealized gains and (losses) on marketable debt securities	4.6	(2.0)
Pension plans	0.7	2.6
Tax effect	(0.1)	(0.6)
Net current period OCI, pension plans	0.6	2.0
Foreign currency translation gains	9.4	77.8
Net other comprehensive (loss) income	3.0	75.3
Comprehensive income	$ 632.0	$ 587.4