Components of Comprehensive Income, Net of Related Tax (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 512.1	$ 310.3
Other comprehensive (loss) income (OCI):
Unrealized losses on derivative contracts	(4.1)	(13.6)
Unrealized gains on derivative contracts, tax	1.6	4.0
Net current period OCI, unrealized (losses) gain on derivative contracts	(2.5)	(9.6)
Unrealized (losses) gains on marketable debt securities	(2.6)	3.4
Unrealized gains (losses) on marketable debt securities, tax	0.6	(1.3)
Net current period OCI, unrealized (losses) gains on marketable debt securities	(2.0)	2.1
Pension plans, before tax	2.6	3.9
Pension plans, tax	(0.6)	(1.3)
Net current period OCI, pension plans	2.0	2.6
Foreign currency translation gains	77.8	75.0
Net other comprehensive income (loss)	75.3	70.1
Comprehensive income	$ 587.4	$ 380.4