ACCUMULATED OTHER COMPREHENSIVE LOSS - Summary of Activity for Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
AOCI Attributable to Parent, Net of Tax
Beginning balance	$ 3,839.1	$ 3,901.1	$ 4,148.3	$ 3,500.3	$ 3,447.5	$ 3,140.4
Other comprehensive gain (loss) before reclassifications	(16.7)	12.3	24.1	6.1	9.2	9.7
Amounts reclassified from accumulated other comprehensive loss	(7.0)	(8.6)	(10.4)	(17.2)	(9.9)	(8.6)
Deferred income tax benefit (expense)	11.9	2.2	(9.7)	(6.5)	3.7	(3.8)
Ending balance	4,210.3	3,839.1	3,901.1	3,814.8	3,500.3	3,447.5
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax
Beginning balance	(150.8)	(152.5)	(154.8)	(147.2)	(156.7)	(143.6)
Other comprehensive gain (loss) before reclassifications	8.1	1.2	11.6	(17.8)	10.4	(10.2)
Amounts reclassified from accumulated other comprehensive loss	(1.6)	(1.6)	(1.7)	(1.7)	(1.7)	(1.6)
Deferred income tax benefit (expense)	4.1	2.1	(7.6)	(4.0)	0.8	(1.3)
Ending balance	(140.2)	(150.8)	(152.5)	(170.7)	(147.2)	(156.7)
Unrealized Gain (Loss) on Hedges
AOCI Attributable to Parent, Net of Tax
Beginning balance	11.8	19.1	12.5	21.8	30.8	23.6
Other comprehensive gain (loss) before reclassifications	(24.3)	(3.7)	19.0	23.5	(4.0)	15.6
Amounts reclassified from accumulated other comprehensive loss	(5.5)	(7.2)	(8.6)	(15.5)	(8.5)	(7.0)
Deferred income tax benefit (expense)	7.6	3.6	(3.8)	(2.4)	3.5	(1.4)
Ending balance	(10.4)	11.8	19.1	27.4	21.8	30.8
Unrealized Gain (Loss) on Available-for-sale Investments
AOCI Attributable to Parent, Net of Tax
Beginning balance	8.5	(3.0)	1.7	0.8	(1.7)	(5.0)
Other comprehensive gain (loss) before reclassifications	(0.6)	14.8	(6.3)	0.6	2.8	4.4
Amounts reclassified from accumulated other comprehensive loss	0.1	0.2	(0.1)	0.0	0.3	0.0
Deferred income tax benefit (expense)	0.2	(3.5)	1.7	(0.1)	(0.6)	(1.1)
Ending balance	8.2	8.5	(3.0)	1.3	0.8	(1.7)
Unrealized Pension Costs
AOCI Attributable to Parent, Net of Tax
Beginning balance	(15.6)	(15.6)	(15.4)	(13.6)	(13.6)	(13.5)
Other comprehensive gain (loss) before reclassifications	0.1	0.0	(0.2)	(0.2)	0.0	(0.1)
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0	0.0	0.0	0.0
Deferred income tax benefit (expense)	0.0	0.0	0.0	0.0	0.0	0.0
Ending balance	(15.5)	(15.6)	(15.6)	(13.8)	(13.6)	(13.6)
Total Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax
Beginning balance	(146.1)	(152.0)	(156.0)	(138.2)	(141.2)	(138.5)
Ending balance	$ (157.9)	$ (146.1)	$ (152.0)	$ (155.8)	$ (138.2)	$ (141.2)