SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION - Cash Flow Information (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Supplemental Cash Flow Information [Abstract]
Property, Plant and Equipment, Additions		$ 102.3	$ 184.7	$ 333.0	$ 505.6
Non-cash accruals				(88.4)	26.1
Right-of-use assets - finance leases				42.5	29.3
Grants				0.0	(10.5)
Cash paid for capital expenditures including deposits				378.9	460.7
Taxes paid on income				3.2	0.1
Income tax refunds				(119.3)	(117.9)
Interest paid on debt obligations net of capitalized interest	[1]			106.0	71.9
Interest Costs Capitalized		$ 14.7	$ 7.0	$ 38.0	$ 16.9

[1] ¹ Capitalized interest was $38.0 million and $16.9 million for the nine months ended September 30, 2020 and 2019, respectively.