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Regulatory Matters	3 Months Ended
Regulatory Matters	Mar. 31, 2022
Regulated Operations [Abstract]
Public Utilities Disclosure [Text Block]	Regulatory Matters Federal Energy Regulatory Commission (FERC) Financial Audit We are subject to FERC’s jurisdiction and regulations with respect to rates for electric transmission service in interstate commerce and electricity sold at wholesale rates, the issuance of certain securities, and incurrence of certain long-term debt, among other things. The Division of Audits and Accounting in the Office of Enforcement of FERC initiated a routine audit of NorthWestern Corporation for the period of January 1, 2018 to the present to evaluate our compliance with FERC accounting and financial reporting requirements. We responded to several sets of data requests as part of the audit process and in April 2022 received a draft audit report from FERC. Based on review of the draft report, we believe final resolution of the identified audit findings and recommendations will not have a material financial impact on us.