FAIR VALUE MEASUREMENTS - Summary of Nuclear Trust Investments (Details) - Spent Nuclear Fuel and Decommissioning Trusts - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	$ 4,916	$ 4,395
Gross unrealized gains	2,649	2,298
Gross unrealized losses	(9)	(15)
Other than temporary impairments	(21)	(26)
INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	4,916	4,395
Gross unrealized gains	2,649	2,298
Gross unrealized losses	(9)	(15)
Other than temporary impairments	(21)	(26)
Cash and Cash Equivalents
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	29	24
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Other than temporary impairments	0	0
Cash and Cash Equivalents \| INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	29	24
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Other than temporary impairments	0	0
United States Government
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	1,351	1,323
Gross unrealized gains	22	8
Gross unrealized losses	(1)	(5)
Other than temporary impairments	(15)	(20)
United States Government \| INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	1,351	1,323
Gross unrealized gains	22	8
Gross unrealized losses	(1)	(5)
Other than temporary impairments	(15)	(20)
Corporate Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	376	210
Gross unrealized gains	6	1
Gross unrealized losses	(7)	(10)
Other than temporary impairments	(6)	(6)
Corporate Debt \| INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	376	210
Gross unrealized gains	6	1
Gross unrealized losses	(7)	(10)
Other than temporary impairments	(6)	(6)
Subtotal Fixed Income Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	1,727	1,533
Gross unrealized gains	28	9
Gross unrealized losses	(8)	(15)
Other than temporary impairments	(21)	(26)
Subtotal Fixed Income Securities \| INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	1,727	1,533
Gross unrealized gains	28	9
Gross unrealized losses	(8)	(15)
Other than temporary impairments	(21)	(26)
Equity Securities - Domestic
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	3,160	2,838
Gross unrealized gains	2,621	2,289
Gross unrealized losses	(1)	0
Other than temporary impairments	0	0
Equity Securities - Domestic \| INDIANA MICHIGAN POWER COMPANY
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value	3,160	2,838
Gross unrealized gains	2,621	2,289
Gross unrealized losses	(1)	0
Other than temporary impairments	$ 0	$ 0

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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