OTHER COMPREHENSIVE INCOME/(LOSS) - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Currency translation differences on investments in foreign subsidiaries	$ 63.8	$ (292.9)	$ 118.9	$ (360.1)
Other comprehensive income/(loss), net	0.8	0.3	5.2	0.5
Other comprehensive income/(loss)	64.6	(292.6)	124.1	(359.6)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	15,930.2	15,986.2	15,843.5	16,168.0
Other comprehensive income/(loss), net of tax	64.6	(292.6)	124.1	(359.6)
Ending balance	15,866.7	15,794.8	15,866.7	15,794.8
Foreign currency translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Currency translation differences on investments in foreign subsidiaries	63.8	(292.9)	118.9	(360.1)
Other comprehensive income/(loss), net	0.0		0.0
Other comprehensive income/(loss)	63.8	(292.9)	118.9	(360.1)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(759.9)	(419.1)	(815.0)	(351.9)
Other comprehensive income/(loss), net of tax	63.8	(292.9)	118.9	(360.1)
Ending balance	(696.1)	(712.0)	(696.1)	(712.0)
Employee benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Currency translation differences on investments in foreign subsidiaries	0.0	0.0	0.0	0.0
Other comprehensive income/(loss), net	0.8		5.2	0.5
Other comprehensive income/(loss)	0.8	0.3	5.2	0.5
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(123.0)	(89.4)	(127.4)	(89.6)
Other comprehensive income/(loss), net of tax	0.8	0.3	5.2	0.5
Ending balance	(122.2)	(89.1)	(122.2)	(89.1)
Total
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income/(loss)	64.6	(292.6)	124.1	(359.6)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(882.9)	(508.5)	(942.4)	(441.5)
Other comprehensive income/(loss), net of tax	64.6	(292.6)	124.1	(359.6)
Ending balance	$ (818.3)	$ (801.1)	$ (818.3)	$ (801.1)