Accumulated Other Comprehensive Income - Tax Effects on Each Component of Accumulated Other Comprehensive Income Recognized in Statements of Comprehensive Income (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]
Foreign currency cumulative translation adjustments, Before Tax	$ (45.4)	$ 145.0	$ (136.0)	$ 414.6
Unrealized cash flow hedge gains (losses), Before Tax	38.1	(35.9)	67.7	(99.0)
Reclassification adjustments on cash flow hedges, Before Tax	5.0	5.2	26.9	(11.6)
Adjustments to prior service cost and unrecognized actuarial assumptions, Before Tax	1.0	0.5	1.0	(2.9)
Total Other Comprehensive Income (Loss), Before Tax	(1.3)	114.8	(40.4)	301.1
Foreign currency cumulative translation adjustments, Tax	(1.4)	15.3	(9.0)	46.7
Unrealized cash flow hedge gains (losses), Tax	5.3	(7.6)	9.7	(19.6)
Reclassification adjustments on cash flow hedges, Tax	0.9	1.1	3.9	(2.2)
Adjustments to prior service cost and unrecognized actuarial assumptions, Tax	(1.0)	1.5	(3.0)	2.1
Total Other Comprehensive Income (Loss), Tax	3.8	10.3	1.6	27.0
Foreign currency cumulative translation adjustments, net of tax	(44.0)	129.7	(127.0)	367.9
Unrealized cash flow hedge gains (losses), net of tax	32.8	(28.3)	58.0	(79.4)
Reclassification adjustments on cash flow hedges, net of tax	4.1	4.1	23.0	(9.4)
Adjustments to prior service cost and unrecognized actuarial assumptions, net of tax	2.0	(1.0)	4.0	(5.0)
Total Other Comprehensive Income (Loss)	$ (5.1)	$ 104.5	$ (42.0)	$ 274.1