{"cik":1993004,"taxonomy":"us-gaap","tag":"LongTermDebt","label":"Long-term Debt","description":"Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.","entityName":"NORTHWESTERN ENERGY GROUP, INC.","units":{"USD":[{"end":"2022-12-31","val":2618882000,"accn":"0001993004-24-000006","fy":2023,"fp":"FY","form":"10-K","filed":"2024-02-15","frame":"CY2022Q4I"},{"end":"2023-12-31","val":2784585000,"accn":"0001993004-24-000006","fy":2023,"fp":"FY","form":"10-K","filed":"2024-02-15"},{"end":"2023-12-31","val":2784585000,"accn":"0001993004-25-000021","fy":2024,"fp":"FY","form":"10-K","filed":"2025-02-13","frame":"CY2023Q4I"},{"end":"2024-12-31","val":2995293000,"accn":"0001993004-25-000021","fy":2024,"fp":"FY","form":"10-K","filed":"2025-02-13"},{"end":"2024-12-31","val":2995293000,"accn":"0001993004-26-000006","fy":2025,"fp":"FY","form":"10-K","filed":"2026-02-12","frame":"CY2024Q4I"},{"end":"2025-12-31","val":3286007000,"accn":"0001993004-26-000006","fy":2025,"fp":"FY","form":"10-K","filed":"2026-02-12","frame":"CY2025Q4I"}]}}