Cover page Cover page - USD ($)

12 Months Ended

Dec. 31, 2022

Feb. 10, 2023

Jun. 30, 2022

Cover [Abstract]

Document Type

10-K

Document Annual Report

true

Document Period End Date

Dec. 31, 2022

Document Transition Report

false

Entity File Number

1-10499

Entity Registrant Name

NORTHWESTERN CORP

Entity Central Index Key

0000073088

Current Fiscal Year End Date

--12-31

Document Fiscal Year Focus

2022

Document Fiscal Period Focus

FY

Amendment Flag

false

Entity Incorporation, State or Country Code

DE

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

Title of 12(b) Security

Common stock

Trading Symbol

NWE

Security Exchange Name

NASDAQ

Entity Well-known Seasoned Issuer

Yes

Entity Voluntary Filers

No

Entity Current Reporting Status

Yes

Entity Interactive Data Current

Yes

Entity Filer Category

Large Accelerated Filer

Entity Small Business

false

Entity Emerging Growth Company

false

ICFR Auditor Attestation Flag

true

Entity Shell Company

false

Entity Public Float

$ 3,308,859,038

Entity Common Stock, Shares Outstanding

59,768,222

Documents Incorporated by Reference

Documents Incorporated by Reference

Certain sections of our Proxy Statement for the 2023 Annual Meeting of Shareholders are incorporated by reference into Part III of this Form 10-K