Components of Comprehensive Income, Net of Related Tax (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 559.6	$ 373.0	$ 1,071.7	$ 683.3
Other comprehensive income (loss) (OCI):
Unrealized gains (losses) on derivative contracts	6.8	11.6	2.7	(2.0)
Unrealized gains on derivative contracts, tax	(2.0)	(3.1)	(0.4)	0.9
Net current period OCI, unrealized (losses) gain on derivative contracts	4.8	8.5	2.3	(1.1)
Unrealized gains (losses) on marketable debt securities	0.5	(0.5)	(2.1)	2.9
Unrealized gains (losses) on marketable debt securities, tax	(0.1)	0.1	0.5	(1.2)
Net current period OCI, unrealized (losses) gains on marketable debt securities	0.4	(0.4)	(1.6)	1.7
Pension plans, before tax	21.3	(1.4)	23.9	2.5
Pension plans, tax	(5.2)	0.0	(5.8)	(1.3)
Net current period OCI, pension plans	16.1	(1.4)	18.1	1.2
Foreign currency translation (losses) gains	(196.7)	126.1	(118.9)	201.1
Net other comprehensive (loss) income	(175.4)	132.8	(100.1)	202.9
Comprehensive income	$ 384.2	$ 505.8	$ 971.6	$ 886.2