ASSET RETIREMENT OBLIGATIONS (Reconciliations of Asset Retirement Obligations) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
ASSET RETIREMENT OBLIGATIONS [Abstract]
Balance at beginning of period	$ 319.7	$ 285.4	$ 315.2	$ 283.2
Liabilities incurred	0.0	0.0	2.3	0.9
Liabilities settled	(2.0)	(2.2)	(3.3)	(5.0)
Accretion expense	3.6	3.2	7.1	6.5
Revisions, net	(0.2)	0.0	(0.2)	0.8
Balance at end of period	$ 321.1	$ 286.4	$ 321.1	$ 286.4