{"cik":52485,"taxonomy":"us-gaap","tag":"OtherLiabilitiesNoncurrent","label":"Other Liabilities, Noncurrent","description":"Amount of liabilities classified as other, due after one year or the normal operating cycle, if longer.","entityName":"INTERSTATE POWER & LIGHT CO","units":{"USD":[{"end":"2025-12-31","val":984000000,"accn":"0000352541-26-000043","fy":2026,"fp":"Q2","form":"10-Q","filed":"2026-07-31","frame":"CY2025Q4I"},{"end":"2026-06-30","val":1013000000,"accn":"0000352541-26-000043","fy":2026,"fp":"Q2","form":"10-Q","filed":"2026-07-31","frame":"CY2026Q2I"}]}}