FAIR VALUE MEASUREMENTS - Fixed Income Securities Held in Nuclear Trusts (Details) - Spent Nuclear Fuel and Decommissioning Trusts $ in Millions	Dec. 31, 2025 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Within 1 year	$ 402
After 1 year through 5 years	709
After 5 years through 10 years	223
After 10 years	393
Total	1,727
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Within 1 year	402
After 1 year through 5 years	709
After 5 years through 10 years	223
After 10 years	393
Total	$ 1,727

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