v3.22.2.2
Document and Entity Information Document
Dec. 07, 2022
Cover [Abstract]  
Document Type 8-K
Document Period End Date Dec. 07, 2022
Entity Registrant Name NorthWestern Corporation
Entity Central Index Key 0000073088
Amendment Flag false
Entity Incorporation, State or Country Code DE
Entity File Number 1-10499
Entity Tax Identification Number 46-0172280
Entity Address, Address Line One 3010 W. 69th Street
Entity Address, City or Town Sioux Falls
Entity Address, State or Province SD
Entity Address, Postal Zip Code 57108
City Area Code 605
Local Phone Number 978-2900
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common stock
Trading Symbol NWE
Security Exchange Name NASDAQ
Entity Emerging Growth Company false