{"cik":52485,"taxonomy":"us-gaap","tag":"Assets","label":"Assets","description":"Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.","entityName":"INTERSTATE POWER & LIGHT CO","units":{"USD":[{"end":"2025-06-30","val":23750000000,"accn":"0000352541-26-000043","fy":2026,"fp":"Q2","form":"10-Q","filed":"2026-07-31","frame":"CY2025Q2I"},{"end":"2025-12-31","val":24991000000,"accn":"0000352541-26-000043","fy":2026,"fp":"Q2","form":"10-Q","filed":"2026-07-31","frame":"CY2025Q4I"},{"end":"2026-06-30","val":25318000000,"accn":"0000352541-26-000043","fy":2026,"fp":"Q2","form":"10-Q","filed":"2026-07-31","frame":"CY2026Q2I"}]}}