OTHER CURRENT ASSETS & OTHER CURRENT LIABILITIES - Other Current Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Other Current Assets and Other Current Liabilities [Abstract]
Value - added tax receivables	$ 260.1	$ 236.4
Prepaid expenses	95.4	78.1
Other tax receivables	80.0	73.8
Sundry receivables	74.1	138.4
Assets held for sale	47.4	47.3
Current financial assets at amortized cost	30.9	40.6
Held-to-maturity investments	0.0	24.2
Other	37.9	24.1
Total other current assets	$ 625.8	$ 662.9