FAIR VALUE MEASUREMENTS - Fixed Income Securities Held in Nuclear Trusts (Details) - Spent Nuclear Fuel and Decommissioning Trusts $ in Millions	Mar. 31, 2026 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Within 1 year	$ 379
After 1 year through 5 years	731
After 5 years through 10 years	251
After 10 years	369
Total	1,730
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Within 1 year	379
After 1 year through 5 years	731
After 5 years through 10 years	251
After 10 years	369
Total	$ 1,730

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