COMPREHENSIVE INCOME - CHANGES IN AOCI (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated other comprehensive income (loss) rollforward [Roll Forward]
Beginning Balance	$ 5,133.0	$ 6,627.9	$ 8,125.9
Amounts reclassified from accumulated other comprehensive income, net of tax	5.1	(30.2)	7.5
Net (decrease) increase in other comprehensive income	(120.3)	(187.5)	415.0
Ending Balance	5,094.9	5,133.0	6,627.9
Total
Accumulated other comprehensive income (loss) rollforward [Roll Forward]
Beginning Balance	(478.7)	(291.0)	(705.7)
Net (decrease) increase in other comprehensive income	(121.0)	(187.7)	414.7
Ending Balance	(599.7)	(478.7)	(291.0)
Total \| Excluding Net Investment Hedge [Member]
Accumulated other comprehensive income (loss) rollforward [Roll Forward]
Beginning Balance	(478.7)	(291.0)
Other comprehensive (loss) income before reclassifications and tax impact	(141.7)	(111.1)
Tax benefit (expense)	15.6	(46.4)
Other comprehensive (loss) income, net of tax, before reclassifications	(126.1)	(157.5)
Amounts reclassified from accumulated other comprehensive income, net of tax	5.1	(30.2)
Net (decrease) increase in other comprehensive income	(121.0)	(187.7)
Ending Balance	(599.7)	(478.7)	(291.0)
Foreign Currency Translation Gain (Loss) \| Excluding Net Investment Hedge [Member]
Accumulated other comprehensive income (loss) rollforward [Roll Forward]
Beginning Balance	(284.7)	(104.5)
Other comprehensive (loss) income before reclassifications and tax impact	(87.8)	(160.1)
Tax benefit (expense)	4.2	(20.1)
Other comprehensive (loss) income, net of tax, before reclassifications	(83.6)	(180.2)
Amounts reclassified from accumulated other comprehensive income, net of tax	0.0	0.0
Net (decrease) increase in other comprehensive income	(83.6)	(180.2)
Ending Balance	(368.3)	(284.7)	(104.5)
Gain and (Loss) on Cash Flow Hedges \| Excluding Net Investment Hedge [Member]
Accumulated other comprehensive income (loss) rollforward [Roll Forward]
Beginning Balance	0.6	(12.6)
Other comprehensive (loss) income before reclassifications and tax impact	(16.9)	5.1
Tax benefit (expense)	4.3	(1.6)
Other comprehensive (loss) income, net of tax, before reclassifications	(12.6)	3.5
Amounts reclassified from accumulated other comprehensive income, net of tax	1.4	9.7
Net (decrease) increase in other comprehensive income	(11.2)	13.2
Ending Balance	(10.6)	0.6	(12.6)
Gain and (Loss) on Net Investment Hedges \| Excluding Net Investment Hedge [Member]
Accumulated other comprehensive income (loss) rollforward [Roll Forward]
Beginning Balance	(111.4)	(127.6)
Other comprehensive (loss) income before reclassifications and tax impact	17.7	36.2
Tax benefit (expense)	(7.0)	(20.0)
Other comprehensive (loss) income, net of tax, before reclassifications	10.7	16.2
Amounts reclassified from accumulated other comprehensive income, net of tax	0.0	0.0
Net (decrease) increase in other comprehensive income	10.7	16.2
Ending Balance	(100.7)	(111.4)	(127.6)
Net Unrealized Holding Gain on Available-for-Sale Securities \| Excluding Net Investment Hedge [Member]
Accumulated other comprehensive income (loss) rollforward [Roll Forward]
Beginning Balance	0.0	44.3
Other comprehensive (loss) income before reclassifications and tax impact		0.0
Tax benefit (expense)		0.0
Other comprehensive (loss) income, net of tax, before reclassifications		0.0
Amounts reclassified from accumulated other comprehensive income, net of tax		(44.3)
Net (decrease) increase in other comprehensive income		(44.3)
Ending Balance		0.0	44.3
Pension Liability Gain (Loss) \| Excluding Net Investment Hedge [Member]
Accumulated other comprehensive income (loss) rollforward [Roll Forward]
Beginning Balance	(83.2)	(90.6)
Other comprehensive (loss) income before reclassifications and tax impact	(54.7)	7.7
Tax benefit (expense)	14.1	(4.7)
Other comprehensive (loss) income, net of tax, before reclassifications	(40.6)	3.0
Amounts reclassified from accumulated other comprehensive income, net of tax	3.7	4.4
Net (decrease) increase in other comprehensive income	(36.9)	7.4
Ending Balance	$ (120.1)	$ (83.2)	$ (90.6)

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