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FAIR VALUE MEASUREMENTS - Securities Activity (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Purchases of Investments $ 2,922.5 $ 2,863.6 $ 2,784.2
INDIANA MICHIGAN POWER COMPANY      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Purchases of Investments 2,902.4 2,845.1 2,765.4
Spent Nuclear Fuel and Decommissioning Trusts      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Proceeds from Investment Sales 2,851.2 2,787.5 2,713.6
Purchases of Investments 2,902.4 2,845.1 2,765.4
Gross Realized Gains on Investment Sales 125.5 99.0 52.4
Gross Realized Losses on Investment Sales 11.5 26.6 42.6
Spent Nuclear Fuel and Decommissioning Trusts | INDIANA MICHIGAN POWER COMPANY      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Proceeds from Investment Sales 2,851.2 2,787.5 2,713.6
Purchases of Investments 2,902.4 2,845.1 2,765.4
Gross Realized Gains on Investment Sales 125.5 99.0 52.4
Gross Realized Losses on Investment Sales $ 11.5 $ 26.6 $ 42.6