OTHER ASSETS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Other Assets [Abstract]
Supply contracts	$ 1,091.0	$ 1,137.9	$ 1,091.0	$ 1,137.9	$ 1,122.9
Other	74.9	41.8	74.9	41.8	68.4
Other assets	1,165.9	1,179.7	1,165.9	1,179.7	$ 1,191.3
2020 Supply Contract Payment				461.0
2020 Supply Contract Payment Accretion Expense				4.0
Payments under other long-term supply contracts			0.0	75.8
Amortization of Supply Contracts	$ 17.3	$ 11.0	$ 34.8	$ 33.3