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Asset Retirement Obligations (ARO) (Tables)
3 Months Ended
Mar. 31, 2025
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Reconciliation of Beginning and Ending Aggregate Carrying Amount of Asset Retirement Obligation
A reconciliation of the beginning and ending aggregate carrying amount of the ARO is shown in the following table.
 
(Millions of dollars)March 31,
2025
December 31,
2024
Balance at beginning of period$49.1 $46.1 
Accretion expense0.9 3.2 
Settlements of liabilities(0.7)(3.1)
Liabilities incurred— 2.9 
Balance at end of period$49.3 $49.1