v3.26.1
Asset Retirement Obligations (ARO) (Tables)
6 Months Ended
Jun. 30, 2026
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)June 30,
2026
December 31,
2025
Balance at beginning of period$52.5 $49.1 
Accretion expense1.8 3.4 
Settlements of liabilities(0.2)(1.0)
Liabilities incurred0.3 1.0 
Balance at end of period$54.4 $52.5