FAIR VALUE MEASUREMENTS - Fair Value of Assets and Liabilities on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Assets:
Restricted Cash	$ 33	$ 71
Total Other Temporary Investments and Restricted Cash	243	291
Total Risk Management Assets	479	617
Total Spent Nuclear Fuel and Decommissioning Trusts	4,803	4,916
Total Assets	5,525	5,824
Liabilities:
Total Risk Management Liabilities	295	310
Commodity
Assets:
Total Risk Management Assets	378	513
Liabilities:
Total Risk Management Liabilities	240	274
Commodity Contract, Cash Flow Hedging
Assets:
Total Risk Management Assets	101	104
Liabilities:
Total Risk Management Liabilities	22	6
Fair Value Hedge Instruments
Liabilities:
Total Risk Management Liabilities	33	30
AEP TEXAS INC.
Assets:
Restricted Cash	6	14
Total Risk Management Assets	0	0
Total Assets	6
Liabilities:
Total Risk Management Liabilities	0	0
AEP TEXAS INC. | Commodity
Assets:
Total Risk Management Assets	0
APPALACHIAN POWER COMPANY
Assets:
Restricted Cash	12	18
Total Risk Management Assets	22	82
Total Assets	34	100
Liabilities:
Total Risk Management Liabilities	7	3
APPALACHIAN POWER COMPANY | Commodity
Assets:
Total Risk Management Assets	22	82
Liabilities:
Total Risk Management Liabilities	7	3
INDIANA MICHIGAN POWER COMPANY
Assets:
Total Risk Management Assets	3	10
Total Spent Nuclear Fuel and Decommissioning Trusts	4,803	4,916
Total Assets	4,806	4,926
Liabilities:
Total Risk Management Liabilities	0	0
INDIANA MICHIGAN POWER COMPANY | Commodity
Assets:
Total Risk Management Assets	3	10
Liabilities:
Total Risk Management Liabilities	0	0
OHIO POWER COMPANY
Assets:
Total Risk Management Assets	0	0
Liabilities:
Total Risk Management Liabilities	32	33
OHIO POWER COMPANY | Commodity
Assets:
Total Risk Management Assets	0
Liabilities:
Total Risk Management Liabilities	32	33
PUBLIC SERVICE COMPANY OF OKLAHOMA
Assets:
Total Risk Management Assets	21	42
Liabilities:
Total Risk Management Liabilities	35	28
PUBLIC SERVICE COMPANY OF OKLAHOMA | Commodity
Assets:
Total Risk Management Assets	21	42
Liabilities:
Total Risk Management Liabilities	35	28
SOUTHWESTERN ELECTRIC POWER COMPANY
Assets:
Restricted Cash	7	15
Total Risk Management Assets	15	35
Total Assets	22	50
Liabilities:
Total Risk Management Liabilities	13	11
SOUTHWESTERN ELECTRIC POWER COMPANY | Commodity
Assets:
Total Risk Management Assets	15	35
Liabilities:
Total Risk Management Liabilities	13	11
Other
Assets:
Total Other Temporary Investments and Restricted Cash	19	36
Risk management asset, offset	(853)	(727)
Total Spent Nuclear Fuel and Decommissioning Trusts	14	15
Assets including netting	(820)	(676)
Liabilities:
Risk management liabilities, offset	(808)	(647)
Other | Commodity
Assets:
Risk management asset, offset	(841)	(713)
Liabilities:
Risk management liabilities, offset	(797)	(633)
Other | Commodity Contract, Cash Flow Hedging
Assets:
Risk management asset, offset	(12)	(14)
Liabilities:
Risk management liabilities, offset	(11)	(14)
Other | Fair Value Hedge Instruments
Liabilities:
Risk management liabilities, offset	0	0
Other | AEP TEXAS INC.
Assets:
Restricted Cash	0	0
Risk management asset, offset	(1)
Other | AEP TEXAS INC. | Commodity
Assets:
Risk management asset, offset	(1)
Other | APPALACHIAN POWER COMPANY
Assets:
Restricted Cash	0	0
Risk management asset, offset	(4)	(2)
Other | APPALACHIAN POWER COMPANY | Commodity
Assets:
Risk management asset, offset	(4)	(2)
Liabilities:
Risk management liabilities, offset	(3)	(3)
Other | INDIANA MICHIGAN POWER COMPANY
Assets:
Total Spent Nuclear Fuel and Decommissioning Trusts	14	15
Assets including netting	2	4
Other | INDIANA MICHIGAN POWER COMPANY | Commodity
Assets:
Risk management asset, offset	(12)	(11)
Liabilities:
Risk management liabilities, offset	(17)	(11)
Other | OHIO POWER COMPANY | Commodity
Assets:
Risk management asset, offset	(1)
Liabilities:
Risk management liabilities, offset	0	0
Other | PUBLIC SERVICE COMPANY OF OKLAHOMA | Commodity
Assets:
Risk management asset, offset	(1)	(2)
Liabilities:
Risk management liabilities, offset	0	(2)
Other | SOUTHWESTERN ELECTRIC POWER COMPANY
Assets:
Restricted Cash	0	0
Risk management asset, offset	(2)	(2)
Other | SOUTHWESTERN ELECTRIC POWER COMPANY | Commodity
Assets:
Risk management asset, offset	(2)	(2)
Liabilities:
Risk management liabilities, offset	(1)	(2)
Mutual Funds
Assets:
Fixed Income Securities:	161	165
Equity securities, fair value disclosure	38	42
Mutual Funds | Other
Assets:
Fixed Income Securities:	0	0
Equity securities, fair value disclosure	0	0
Subtotal Fixed Income Securities
Assets:
Fixed Income Securities:	1,730	1,727
Subtotal Fixed Income Securities | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	1,730	1,727
Subtotal Fixed Income Securities | Other
Assets:
Fixed Income Securities:	0	0
Subtotal Fixed Income Securities | Other | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	0	0
United States Government
Assets:
Fixed Income Securities:	1,351	1,351
United States Government | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	1,351	1,351
United States Government | Other
Assets:
Fixed Income Securities:	0	0
United States Government | Other | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	0	0
Corporate Debt
Assets:
Fixed Income Securities:	379	376
Corporate Debt | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	379	376
Corporate Debt | Other
Assets:
Fixed Income Securities:	0	0
Corporate Debt | Other | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	0	0
Equity Securities - Domestic
Assets:
Equity securities, fair value disclosure	3,046	3,160
Equity Securities - Domestic | INDIANA MICHIGAN POWER COMPANY
Assets:
Equity securities, fair value disclosure	3,046	3,160
Equity Securities - Domestic | Other
Assets:
Equity securities, fair value disclosure	0	0
Equity Securities - Domestic | Other | INDIANA MICHIGAN POWER COMPANY
Assets:
Equity securities, fair value disclosure	0	0
Restricted Cash | Other
Assets:
Restricted Cash	8	23
Other Cash Deposits
Assets:
Cash and cash equivalents, fair value disclosure	11	13
Other Cash Deposits | Other
Assets:
Cash and cash equivalents, fair value disclosure	11	13
Cash and Cash Equivalents
Assets:
Cash and cash equivalents, fair value disclosure	27	29
Cash and Cash Equivalents | INDIANA MICHIGAN POWER COMPANY
Assets:
Cash and cash equivalents, fair value disclosure	27	29
Cash and Cash Equivalents | Other
Assets:
Cash and cash equivalents, fair value disclosure	14	15
Cash and Cash Equivalents | Other | INDIANA MICHIGAN POWER COMPANY
Assets:
Cash and cash equivalents, fair value disclosure	14	15
Level 1 | Within Current Year
Liabilities:
Maturities of net fair value of risk management contracts	(6)	(2)
Level 1 | Estimate of Fair Value Measurement
Assets:
Restricted Cash	25	48
Total Other Temporary Investments and Restricted Cash	224	255
Risk Management Assets	2	2
Total Spent Nuclear Fuel and Decommissioning Trusts	3,059	3,174
Total Assets	3,285	3,431
Liabilities:
Risk Management Liabilities	8	4
Level 1 | Estimate of Fair Value Measurement | Commodity
Assets:
Risk Management Assets	2	2
Liabilities:
Risk Management Liabilities	8	4
Level 1 | Estimate of Fair Value Measurement | Commodity Contract, Cash Flow Hedging
Assets:
Risk Management Assets	0	0
Liabilities:
Risk Management Liabilities	0	0
Level 1 | Estimate of Fair Value Measurement | Fair Value Hedge Instruments
Liabilities:
Risk Management Liabilities	0	0
Level 1 | Estimate of Fair Value Measurement | AEP TEXAS INC.
Assets:
Restricted Cash	6	14
Total Assets	6
Level 1 | Estimate of Fair Value Measurement | AEP TEXAS INC. | Commodity
Assets:
Risk Management Assets	0
Level 1 | Estimate of Fair Value Measurement | APPALACHIAN POWER COMPANY
Assets:
Restricted Cash	12	18
Total Assets	12	18
Level 1 | Estimate of Fair Value Measurement | APPALACHIAN POWER COMPANY | Commodity
Assets:
Risk Management Assets	0	0
Liabilities:
Risk Management Liabilities	0	0
Level 1 | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Total Spent Nuclear Fuel and Decommissioning Trusts	3,059	3,174
Total Assets	3,059	3,174
Level 1 | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY | Commodity
Assets:
Risk Management Assets	0	0
Liabilities:
Risk Management Liabilities	0	0
Level 1 | Estimate of Fair Value Measurement | OHIO POWER COMPANY | Commodity
Assets:
Risk Management Assets	0
Liabilities:
Risk Management Liabilities	0	0
Level 1 | Estimate of Fair Value Measurement | PUBLIC SERVICE COMPANY OF OKLAHOMA | Commodity
Assets:
Risk Management Assets	0	0
Liabilities:
Risk Management Liabilities	0	0
Level 1 | Estimate of Fair Value Measurement | SOUTHWESTERN ELECTRIC POWER COMPANY
Assets:
Restricted Cash	7	15
Total Assets	7	15
Level 1 | Estimate of Fair Value Measurement | SOUTHWESTERN ELECTRIC POWER COMPANY | Commodity
Assets:
Risk Management Assets	0	0
Liabilities:
Risk Management Liabilities	0	0
Level 1 | Mutual Funds | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	161	165
Equity securities, fair value disclosure	38	42
Level 1 | Subtotal Fixed Income Securities | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	0	0
Level 1 | Subtotal Fixed Income Securities | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	0	0
Level 1 | United States Government | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	0	0
Level 1 | United States Government | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	0	0
Level 1 | Corporate Debt | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	0	0
Level 1 | Corporate Debt | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	0	0
Level 1 | Equity Securities - Domestic | Estimate of Fair Value Measurement
Assets:
Equity securities, fair value disclosure	3,046	3,160
Level 1 | Equity Securities - Domestic | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Equity securities, fair value disclosure	3,046	3,160
Level 1 | Other Cash Deposits | Estimate of Fair Value Measurement
Assets:
Cash and cash equivalents, fair value disclosure	0	0
Level 1 | Cash and Cash Equivalents | Estimate of Fair Value Measurement
Assets:
Cash and cash equivalents, fair value disclosure	13	14
Level 1 | Cash and Cash Equivalents | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Cash and cash equivalents, fair value disclosure	13	14
Level 2 | Within Current Year
Liabilities:
Maturities of net fair value of risk management contracts		12
Level 2 | Maturity Period 2
Liabilities:
Maturities of net fair value of risk management contracts	71	65
Level 2 | Maturity Period 3
Liabilities:
Maturities of net fair value of risk management contracts		1
Level 2 | Estimate of Fair Value Measurement
Assets:
Restricted Cash	0	0
Total Other Temporary Investments and Restricted Cash	0	0
Risk Management Assets	1,054	931
Total Spent Nuclear Fuel and Decommissioning Trusts	1,730	1,727
Total Assets	2,784	2,658
Liabilities:
Risk Management Liabilities	951	801
Level 2 | Estimate of Fair Value Measurement | Commodity
Assets:
Risk Management Assets	958	831
Liabilities:
Risk Management Liabilities	887	752
Level 2 | Estimate of Fair Value Measurement | Commodity Contract, Cash Flow Hedging
Assets:
Risk Management Assets	96	100
Liabilities:
Risk Management Liabilities	31	19
Level 2 | Estimate of Fair Value Measurement | Fair Value Hedge Instruments
Liabilities:
Risk Management Liabilities	33	30
Level 2 | Estimate of Fair Value Measurement | AEP TEXAS INC.
Assets:
Restricted Cash	0	0
Total Assets	1
Level 2 | Estimate of Fair Value Measurement | AEP TEXAS INC. | Commodity
Assets:
Risk Management Assets	1
Level 2 | Estimate of Fair Value Measurement | APPALACHIAN POWER COMPANY
Assets:
Restricted Cash	0	0
Total Assets	4	3
Level 2 | Estimate of Fair Value Measurement | APPALACHIAN POWER COMPANY | Commodity
Assets:
Risk Management Assets	4	3
Liabilities:
Risk Management Liabilities	9	6
Level 2 | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Total Spent Nuclear Fuel and Decommissioning Trusts	1,730	1,727
Total Assets	1,742	1,739
Level 2 | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY | Commodity
Assets:
Risk Management Assets	12	12
Liabilities:
Risk Management Liabilities	16	11
Level 2 | Estimate of Fair Value Measurement | OHIO POWER COMPANY | Commodity
Assets:
Risk Management Assets	1
Liabilities:
Risk Management Liabilities	0	0
Level 2 | Estimate of Fair Value Measurement | PUBLIC SERVICE COMPANY OF OKLAHOMA | Commodity
Assets:
Risk Management Assets	1	1
Liabilities:
Risk Management Liabilities	35	28
Level 2 | Estimate of Fair Value Measurement | SOUTHWESTERN ELECTRIC POWER COMPANY
Assets:
Restricted Cash	0	0
Total Assets	1	0
Level 2 | Estimate of Fair Value Measurement | SOUTHWESTERN ELECTRIC POWER COMPANY | Commodity
Assets:
Risk Management Assets	1	0
Liabilities:
Risk Management Liabilities	13	11
Level 2 | Mutual Funds | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	0	0
Equity securities, fair value disclosure	0	0
Level 2 | Subtotal Fixed Income Securities | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	1,730	1,727
Level 2 | Subtotal Fixed Income Securities | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	1,730	1,727
Level 2 | United States Government | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	1,351	1,351
Level 2 | United States Government | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	1,351	1,351
Level 2 | Corporate Debt | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	379	376
Level 2 | Corporate Debt | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	379	376
Level 2 | Equity Securities - Domestic | Estimate of Fair Value Measurement
Assets:
Equity securities, fair value disclosure	0	0
Level 2 | Equity Securities - Domestic | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Equity securities, fair value disclosure	0	0
Level 2 | Other Cash Deposits | Estimate of Fair Value Measurement
Assets:
Cash and cash equivalents, fair value disclosure	0	0
Level 2 | Cash and Cash Equivalents | Estimate of Fair Value Measurement
Assets:
Cash and cash equivalents, fair value disclosure	0	0
Level 2 | Cash and Cash Equivalents | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Cash and cash equivalents, fair value disclosure	0	0
Level 3 | Within Current Year
Liabilities:
Maturities of net fair value of risk management contracts	84	210
Level 3 | Maturity Period 2
Liabilities:
Maturities of net fair value of risk management contracts	50	51
Level 3 | Maturity Period 3
Liabilities:
Maturities of net fair value of risk management contracts	(4)	(6)
Level 3 | Maturity Period 4
Liabilities:
Maturities of net fair value of risk management contracts	(14)	(13)
Level 3 | Estimate of Fair Value Measurement
Assets:
Restricted Cash	0	0
Total Other Temporary Investments and Restricted Cash	0	0
Risk Management Assets	276	411
Total Spent Nuclear Fuel and Decommissioning Trusts	0	0
Total Assets	276	411
Liabilities:
Risk Management Liabilities	144	152
Level 3 | Estimate of Fair Value Measurement | Commodity
Assets:
Risk Management Assets	259	393
Liabilities:
Risk Management Liabilities	142	151
Level 3 | Estimate of Fair Value Measurement | Commodity Contract, Cash Flow Hedging
Assets:
Risk Management Assets	17	18
Liabilities:
Risk Management Liabilities	2	1
Level 3 | Estimate of Fair Value Measurement | Fair Value Hedge Instruments
Liabilities:
Risk Management Liabilities	0	0
Level 3 | Estimate of Fair Value Measurement | AEP TEXAS INC.
Assets:
Restricted Cash	0	0
Total Assets	0
Level 3 | Estimate of Fair Value Measurement | AEP TEXAS INC. | Commodity
Assets:
Risk Management Assets	0
Level 3 | Estimate of Fair Value Measurement | APPALACHIAN POWER COMPANY
Assets:
Restricted Cash	0	0
Total Assets	22	81
Level 3 | Estimate of Fair Value Measurement | APPALACHIAN POWER COMPANY | Commodity
Assets:
Risk Management Assets	22	81
Liabilities:
Risk Management Liabilities	1	0
Level 3 | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Total Spent Nuclear Fuel and Decommissioning Trusts	0	0
Total Assets	3	9
Level 3 | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY | Commodity
Assets:
Risk Management Assets	3	9
Liabilities:
Risk Management Liabilities	1	0
Level 3 | Estimate of Fair Value Measurement | OHIO POWER COMPANY | Commodity
Assets:
Risk Management Assets	0
Liabilities:
Risk Management Liabilities	32	33
Level 3 | Estimate of Fair Value Measurement | PUBLIC SERVICE COMPANY OF OKLAHOMA | Commodity
Assets:
Risk Management Assets	21	43
Liabilities:
Risk Management Liabilities	0	2
Level 3 | Estimate of Fair Value Measurement | SOUTHWESTERN ELECTRIC POWER COMPANY
Assets:
Restricted Cash	0	0
Total Assets	16	37
Level 3 | Estimate of Fair Value Measurement | SOUTHWESTERN ELECTRIC POWER COMPANY | Commodity
Assets:
Risk Management Assets	16	37
Liabilities:
Risk Management Liabilities	1	2
Level 3 | Mutual Funds | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	0	0
Equity securities, fair value disclosure	0	0
Level 3 | Subtotal Fixed Income Securities | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	0	0
Level 3 | Subtotal Fixed Income Securities | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	0	0
Level 3 | United States Government | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	0	0
Level 3 | United States Government | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	0	0
Level 3 | Corporate Debt | Estimate of Fair Value Measurement
Assets:
Fixed Income Securities:	0	0
Level 3 | Corporate Debt | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Fixed Income Securities:	0	0
Level 3 | Equity Securities - Domestic | Estimate of Fair Value Measurement
Assets:
Equity securities, fair value disclosure	0	0
Level 3 | Equity Securities - Domestic | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Equity securities, fair value disclosure	0	0
Level 3 | Other Cash Deposits | Estimate of Fair Value Measurement
Assets:
Cash and cash equivalents, fair value disclosure	0	0
Level 3 | Cash and Cash Equivalents | Estimate of Fair Value Measurement
Assets:
Cash and cash equivalents, fair value disclosure	0	0
Level 3 | Cash and Cash Equivalents | Estimate of Fair Value Measurement | INDIANA MICHIGAN POWER COMPANY
Assets:
Cash and cash equivalents, fair value disclosure	$ 0	$ 0