OTHER CURRENT ASSETS & OTHER CURRENT LIABILITIES - Other Current Assets (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Other Current Assets and Other Current Liabilities [Abstract]
Value - added tax receivables	$ 260.1	$ 256.9
Prepaid expenses	93.5	78.1
Sundry receivables	74.1	138.4
Other tax receivables	61.3	73.8
Current financial assets at amortized cost	37.3	40.6
Assets held for sale	6.2	47.3
Held-to-maturity investments	3.2	24.2
Other	43.0	24.1
Total other current assets	$ 578.7	$ 683.4