OTHER CURRENT ASSETS & OTHER CURRENT LIABILITIES - Other Current Assets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Other Current Assets and Other Current Liabilities [Abstract]
Value - added tax receivables	$ 246.9	$ 256.9
Prepaid expenses	77.2	78.1
Sundry receivables	67.9	138.4
Other tax receivables	61.3	73.8
Current financial assets at amortized cost	36.4	40.6
Assets held for sale	4.0	47.3
Held-to-maturity investments	6.9	24.2
Other	33.3	24.1
Total other current assets	$ 533.9	$ 683.4