FAIR VALUE MEASUREMENTS - Securities Activity (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Purchases of Investments	$ 2,981	$ 2,923	$ 2,864
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Purchases of Investments	2,959	2,902	2,845
Spent Nuclear Fuel and Decommissioning Trusts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from Investment Sales	2,909	2,851	2,788
Purchases of Investments	2,959	2,902	2,845
Gross Realized Gains on Investment Sales	120	126	99
Gross Realized Losses on Investment Sales	5	12	27
Spent Nuclear Fuel and Decommissioning Trusts \| INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from Investment Sales	2,909	2,851	2,788
Purchases of Investments	2,959	2,902	2,845
Gross Realized Gains on Investment Sales	120	126	99
Gross Realized Losses on Investment Sales	$ 5	$ 12	$ 27

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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