EFFECTS OF REGULATION - Regulatory Liabilities - SWEPCO (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
Pays/paying a return | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 54	22
Remaining Refund Period	1 year
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 | Pending final regulatory determination | Income Taxes, Net
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 | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	1,048	1,622
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
Does not pay/paying a return | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 10	32
Remaining Refund Period	1 year
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 | 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 | 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 | Other Regulatory Liabilities Approved for Payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	125	79
SOUTHWESTERN ELECTRIC POWER COMPANY
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	45	22
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	531	611
SOUTHWESTERN ELECTRIC POWER COMPANY | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	7	7
SOUTHWESTERN ELECTRIC POWER COMPANY | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	524	604
SOUTHWESTERN ELECTRIC POWER COMPANY | Pays/paying a return | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 45	22
Remaining Refund Period	1 year
SOUTHWESTERN ELECTRIC POWER COMPANY | Pays/paying a return | Pending final regulatory determination | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 7	7
SOUTHWESTERN ELECTRIC POWER COMPANY | Pays/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	489	592
SOUTHWESTERN ELECTRIC POWER COMPANY | Pays/paying a return | Approved for payment | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	24	128
SOUTHWESTERN ELECTRIC 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	459	457
SOUTHWESTERN ELECTRIC 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	6	7
SOUTHWESTERN ELECTRIC POWER COMPANY | Does not pay/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	35	12
SOUTHWESTERN ELECTRIC POWER COMPANY | Does not pay/paying a return | Approved for payment | Demand Side Management
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 11	9
Remaining Refund Period	2 years
SOUTHWESTERN ELECTRIC 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	$ 24	$ 3