ASSET RETIREMENT OBLIGATIONS (Tables)

9 Months Ended

Sep. 30, 2022

ASSET RETIREMENT OBLIGATIONS [Abstract]

Asset Retirement Obligations Operating Costs

	Three Months Ended		Nine Months Ended
	September 30		September 30
in millions	2022	2021	2022	2021
ARO Operating Costs
Accretion	$          3.6	$          3.3	$        10.7	$          9.8
Depreciation	2.4	3.0	7.2	8.2
Total	$          6.0	$          6.3	$        17.9	$        18.0

Reconciliations of Asset Retirement Obligations

	Three Months Ended		Nine Months Ended
	September 30		September 30
in millions	2022	2021	2022	2021
Asset Retirement Obligations
Balance at beginning of period	$       321.1	$       286.4	$       315.2	$       283.2
Liabilities incurred	19.2	10.7	21.5	11.7
Liabilities settled	(2.3)	(5.3)	(5.6)	(10.4)
Accretion expense	3.6	3.3	10.7	9.8
Revisions, net	(1.6)	3.2	(1.8)	4.0
Balance at end of period	$       340.0	$       298.3	$       340.0	$       298.3