FAIR VALUE MEASUREMENTS - Securities Activity (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Purchases of Investments	$ 575	$ 603
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Purchases of Investments	573	601
Spent Nuclear Fuel and Decommissioning Trusts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from Investment Sales	548	577
Purchases of Investments	573	601
Gross Realized Gains on Investment Sales	5	2
Gross Realized Losses on Investment Sales	4	1
Spent Nuclear Fuel and Decommissioning Trusts \| INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from Investment Sales	548	577
Purchases of Investments	573	601
Gross Realized Gains on Investment Sales	5	2
Gross Realized Losses on Investment Sales	$ 4	$ 1

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