ASSET RETIREMENT OBLIGATIONS (Tables)

6 Months Ended

Jun. 30, 2022

ASSET RETIREMENT OBLIGATIONS [Abstract]

Asset Retirement Obligations Operating Costs

	Three Months Ended		Six Months Ended
	June 30		June 30
in millions	2022	2021	2022	2021
ARO Operating Costs
Accretion	$          3.6	$          3.2	$          7.1	$          6.5
Depreciation	2.4	2.7	4.8	5.3
Total	$          6.0	$          5.9	$        11.9	$        11.8

Reconciliations of Asset Retirement Obligations

	Three Months Ended		Six Months Ended
	June 30		June 30
in millions	2022	2021	2022	2021
Asset Retirement Obligations
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