ASSET RETIREMENT OBLIGATIONS (Reconciliations of Asset Retirement Obligations) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
ASSET RETIREMENT OBLIGATIONS [Abstract]
Balance at beginning of period	$ 311.9	$ 319.7	$ 311.3	$ 315.2
Liabilities incurred	0.0	0.0	0.0	2.3
Liabilities settled	(3.7)	(2.0)	(6.6)	(3.3)
Accretion expense	3.4	3.6	6.9	7.1
Revisions, net	0.0	(0.2)	0.0	(0.2)
Balance at end of period	$ 311.6	$ 321.1	$ 311.6	$ 321.1