Components of Comprehensive Income, Net of Related Tax (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 545.3	$ 402.7	$ 1,617.0	$ 1,086.0
Other comprehensive (loss) income (OCI):
Unrealized (losses) gains on derivative contracts	(8.9)	1.9	(6.2)	(0.1)
Unrealized gains on derivative contracts, tax	2.5	(0.7)	2.1	0.2
Net current period OCI, unrealized (losses) gain on derivative contracts	(6.4)	1.2	(4.1)	0.1
Unrealized (losses) gains on marketable debt securities	(1.5)	(0.4)	(3.6)	2.5
Unrealized gains (losses) on marketable debt securities, tax	0.4	0.1	0.9	(1.1)
Net current period OCI, unrealized (losses) gains on marketable debt securities	(1.1)	(0.3)	(2.7)	1.4
Pension plans, before tax	10.2	0.6	34.1	3.1
Pension plans, tax	(2.4)	(0.6)	(8.2)	(1.9)
Net current period OCI, pension plans	7.8	0.0	25.9	1.2
Foreign currency translation (losses) gains	(1.6)	108.1	(120.5)	309.2
Net other comprehensive (loss) income	(1.3)	109.0	(101.4)	311.9
Comprehensive income	$ 544.0	$ 511.7	$ 1,515.6	$ 1,397.9