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Commitments and Contingencies (Details) - Westmoreland - NSP-Minnesota
$ in Millions
9 Months Ended
Sep. 30, 2021
USD ($)
Commitments and Contingencies Disclosure [Abstract]  
Gain (Loss) Related to Litigation Settlement $ 36
Public Utilities, General Disclosures [Line Items]  
Gain (Loss) Related to Litigation Settlement $ 36