OTHER COMPREHENSIVE INCOME/(LOSS) - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Currency translation differences on investments in foreign subsidiaries	$ (96.3)	$ 55.1
Other comprehensive income/(loss), net	1.0	4.4
Other comprehensive income/(loss)	(95.3)	59.5
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	15,170.3	15,843.5
Other comprehensive income/(loss), net of tax	(95.3)	59.5
Ending balance	15,185.0	15,930.2
Foreign currency translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Currency translation differences on investments in foreign subsidiaries	(96.3)	55.1
Other comprehensive income/(loss), net	0.0	0.0
Other comprehensive income/(loss)	(96.3)	55.1
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(670.1)	(815.0)
Other comprehensive income/(loss), net of tax	(96.3)	55.1
Ending balance	(766.4)	(759.9)
Employee benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Currency translation differences on investments in foreign subsidiaries	0.0	0.0
Other comprehensive income/(loss), net	1.0	4.4
Other comprehensive income/(loss)	1.0	4.4
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(131.7)	(127.4)
Other comprehensive income/(loss), net of tax	1.0	4.4
Ending balance	(130.7)	(123.0)
Total
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income/(loss)	(95.3)	59.5
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(801.8)	(942.4)
Other comprehensive income/(loss), net of tax	(95.3)	59.5
Ending balance	$ (897.1)	$ (882.9)