Accumulated Other Comprehensive (Loss) Income - Tax Effects on Each Component of Accumulated Other Comprehensive Income Recognized in Statements of Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Foreign currency cumulative translation adjustments, Before Tax	$ (148.7)	$ 396.8	$ (128.2)
Unrealized cash flow hedge gains, Before Tax	81.1	(116.0)	29.7
Reclassification adjustments on foreign currency hedges, Before Tax	26.8	(4.6)	(19.6)
Unrealized gains on securities, Before Tax			0.5
Adjustments to prior service cost and unrecognized actuarial assumptions, Before Tax	(22.7)	6.6	27.3
Total Other Comprehensive Income (Loss), Before Tax	(63.5)	282.8	(90.3)
Foreign currency cumulative translation adjustments, Tax	(13.3)	(48.2)	1.8
Unrealized cash flow hedge gains, Tax	12.9	(21.0)	1.4
Reclassification adjustments on foreign currency hedges, Tax	3.2	(0.8)	6.2
Adjustments to prior service cost and unrecognized actuarial assumptions, Tax	(5.0)	2.0	5.3
Total Other Comprehensive Income (Loss), Tax	(2.2)	(68.0)	14.7
Foreign currency cumulative translation adjustments, net of tax	(135.4)	445.0	(130.0)
Unrealized cash flow hedge gains, net of tax	68.2	(95.0)	28.3
Reclassification adjustments on foreign currency hedges, net of tax	23.6	(3.8)	(25.8)
Unrealized gains on securities, net of tax			0.5
Adjustments to prior service cost and unrecognized actuarial assumptions, net of tax	(17.7)	4.6	22.0
Total Other Comprehensive (Loss) Income	$ (61.3)	$ 350.8	$ (105.0)