ACCUMULATED OTHER COMPREHENSIVE LOSS - Summary of Activity for Each Component of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax
Beginning balance	$ 5,133.3	$ 4,658.4	$ 4,574.3	$ 3,839.1	$ 3,901.1	$ 4,148.3
Other comprehensive gain (loss) before reclassifications	0.9	8.3	(1.2)	(16.7)	12.3	24.1
Amounts reclassified from accumulated other comprehensive loss	10.6	6.8	(1.6)	(7.0)	(8.6)	(10.4)
Deferred income tax (expense) benefit	(7.3)	(2.3)	(8.5)	11.9	2.2	(9.7)
Ending balance	5,541.3	5,133.3	4,658.4	4,210.3	3,839.1	3,901.1
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax
Beginning balance	(144.1)	(154.6)	(122.4)	(150.8)	(152.5)	(154.8)
Other comprehensive gain (loss) before reclassifications	(9.0)	12.9	(30.2)	8.1	1.2	11.6
Amounts reclassified from accumulated other comprehensive loss	(1.6)	(1.5)	(1.6)	(1.6)	(1.6)	(1.7)
Deferred income tax (expense) benefit	(1.6)	(0.9)	(0.4)	4.1	2.1	(7.6)
Ending balance	(156.3)	(144.1)	(154.6)	(140.2)	(150.8)	(152.5)
Unrealized (Loss) Gain on Hedges
AOCI Attributable to Parent, Net of Tax
Beginning balance	(0.8)	(3.2)	(27.7)	11.8	19.1	12.5
Other comprehensive gain (loss) before reclassifications	14.5	(3.4)	34.8	(24.3)	(3.7)	19.0
Amounts reclassified from accumulated other comprehensive loss	10.1	7.2	(0.9)	(5.5)	(7.2)	(8.6)
Deferred income tax (expense) benefit	(6.3)	(1.4)	(9.4)	7.6	3.6	(3.8)
Ending balance	17.5	(0.8)	(3.2)	(10.4)	11.8	19.1
Unrealized Gain on Available-for-sale Investments
AOCI Attributable to Parent, Net of Tax
Beginning balance	4.8	4.7	8.6	8.5	(3.0)	1.7
Other comprehensive gain (loss) before reclassifications	(4.5)	(1.0)	(6.1)	(0.6)	14.8	(6.3)
Amounts reclassified from accumulated other comprehensive loss	2.1	1.1	0.9	0.1	0.2	(0.1)
Deferred income tax (expense) benefit	0.6	0.0	1.3	0.2	(3.5)	1.7
Ending balance	3.0	4.8	4.7	8.2	8.5	(3.0)
Unrealized Pension Costs
AOCI Attributable to Parent, Net of Tax
Beginning balance	(19.5)	(19.3)	(19.6)	(15.6)	(15.6)	(15.4)
Other comprehensive gain (loss) before reclassifications	(0.1)	(0.2)	0.3	0.1	0.0	(0.2)
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0	0.0	0.0	0.0	0.0
Deferred income tax (expense) benefit	0.0	0.0	0.0	0.0	0.0	0.0
Ending balance	(19.6)	(19.5)	(19.3)	(15.5)	(15.6)	(15.6)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax
Beginning balance	(159.6)	(172.4)	(161.1)	(146.1)	(152.0)	(156.0)
Ending balance	$ (155.4)	$ (159.6)	$ (172.4)	$ (157.9)	$ (146.1)	$ (152.0)

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Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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