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ASSET RETIREMENT OBLIGATIONS (Tables)
 6 Months Ended
Jun. 30, 2024
Asset Retirement Obligation Disclosure [Abstract]  
Asset Retirement Obligations Operating Costs
ARO operating costs related to accretion of the liabilities and depreciation of the assets are as follows:
Three Months Ended
June 30		Six Months Ended
June 30
in millions2024202320242023
Accretion$3.6 $3.4 $7.1 $6.9 
Depreciation2.8 2.2 5.2 4.3 
Total ARO operating costs$6.4 $5.6 $12.3 $11.2 
Reconciliations of Asset Retirement Obligations
Reconciliations of the carrying amounts of our AROs are as follows:
Three Months Ended
June 30		Six Months Ended
June 30
in millions2024202320242023
ARO balance at beginning of period$325.7 $311.9 $324.1 $311.3 
Liabilities incurred0.8 0.0 0.8 0.0 
Liabilities settled(3.0)(3.7)(4.8)(6.6)
Accretion expense3.6 3.4 7.1 6.9 
Revisions, net7.0 0.0 6.9 0.0 
ARO balance at end of period$334.1 $311.6 $334.1 $311.6