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Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2020
Asset Retirement Obligation [Abstract]  
Asset Retirement Obligations ASSET RETIREMENT OBLIGATIONS
The following table summarizes the Company’s 2020 and 2019 activity related to asset retirement obligations:
(in millions)20202019
Asset retirement obligation at January 1$57 $61 
Accretion of discount4 3 
Obligations incurred1 2 
Obligations assumed from Montage28 — 
Obligations settled/removed(6)(9)
Revisions of estimates1 — 
Asset retirement obligation at December 31$85 $57 
Current liability$4 $6 
Long-term liability81 51 
Asset retirement obligation at December 31$85 $57