ASSET RETIREMENT OBLIGATIONS (Reconciliations of Asset Retirement Obligations) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
ASSET RETIREMENT OBLIGATIONS [Abstract]
Balance at beginning of period	$ 311.6	$ 321.1	$ 311.3	$ 315.2
Liabilities incurred	0.0	19.2	0.0	21.5
Liabilities settled	(1.9)	(2.3)	(8.4)	(5.6)
Accretion expense	3.5	3.6	10.3	10.7
Revisions, net	2.3	(1.6)	2.3	(1.8)
Balance at end of period	$ 315.5	$ 340.0	$ 315.5	$ 340.0