EFFECTS OF REGULATION - Regulatory Liabilities - I&M (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 64	$ 54
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	8,362	8,344
Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	119	322
Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	8,243	8,022
Does not pay/paying a return | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	29	146
Does not pay/paying a return | Pending final regulatory determination | FERC 2021 Transmission Formula Rate Challenge Refunds
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	0	131
Does not pay/paying a return | Pending final regulatory determination | Other Regulatory Liabilities Pending Final Regulatory Determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	29	15
Does not pay/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	3,047	2,496
Does not pay/paying a return | Approved for payment | Other Regulatory Liabilities Approved for Payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	125	79
Does not pay/paying a return | Approved for payment | Excess Nuclear Decommissioning Funding
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,557	2,137
Does not pay/paying a return | Approved for payment | Spent Nuclear Fuel
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 51	50
Does not pay/paying a return | Approved for payment | PJM Costs and Off-system Sales Margin Sharing - Indiana
Regulatory Liability [Line Items]
Remaining Refund Period	2 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 40	2
Does not pay/paying a return | Approved for payment | Demand Side Management
Regulatory Liability [Line Items]
Remaining Refund Period	2 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 54	53
Does not pay/paying a return | Approved for payment | Deferred Investment Tax Credits
Regulatory Liability [Line Items]
Remaining Refund Period	25 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 64	65
Pays/paying a return | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	90	176
Pays/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	5,196	5,526
Pays/paying a return | Approved for payment | Asset Removal Costs
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	4,023	3,828
Pays/paying a return | Approved for payment | Other Regulatory Liabilities Approved for Payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	39	40
INDIANA MICHIGAN POWER COMPANY
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	19	10
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,938	2,481
INDIANA MICHIGAN POWER COMPANY | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	27	44
INDIANA MICHIGAN POWER COMPANY | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,911	2,437
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Under-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 10	10
Remaining Refund Period	1 year
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 27	44
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Pending final regulatory determination | Cook Plant PTC Deferral - Michigan
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	26	15
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Pending final regulatory determination | FERC 2021 Transmission Formula Rate Challenge Refunds
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	0	29
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Pending final regulatory determination | Other Regulatory Liabilities Pending Final Regulatory Determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	1	0
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,710	2,239
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Other Regulatory Liabilities Approved for Payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	8	3
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Excess Nuclear Decommissioning Funding
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	2,557	2,137
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Spent Nuclear Fuel
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 51	50
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | PJM Costs and Off-system Sales Margin Sharing - Indiana
Regulatory Liability [Line Items]
Remaining Refund Period	2 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 35	2
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Demand Side Management
Regulatory Liability [Line Items]
Remaining Refund Period	2 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 31	33
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Pension and OPEB Funded Status
Regulatory Liability [Line Items]
Remaining Refund Period	12 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 15	0
INDIANA MICHIGAN POWER COMPANY | Does not pay/paying a return | Approved for payment | Deferred Investment Tax Credits
Regulatory Liability [Line Items]
Remaining Refund Period	25 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 13	14
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Under-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 9	0
Remaining Refund Period	1 year
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 201	198
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Approved for payment | Asset Removal Costs
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 172	174
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Approved for payment | Renewable Energy Surcharge - Michigan
Regulatory Liability [Line Items]
Remaining Refund Period	2 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 22	24
INDIANA MICHIGAN POWER COMPANY | Pays/paying a return | Approved for payment | Other Regulatory Liabilities Approved for Payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 7	$ 0