FAIR VALUE MEASUREMENTS - Narrative (Details) - Spent Nuclear Fuel and Decommissioning Trusts - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjusted cost of debt securities	$ 1,700	$ 1,500
Adjusted cost of equity securities	540	549
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjusted cost of debt securities	1,700	1,500
Adjusted cost of equity securities	$ 540	$ 549