EFFECTS OF REGULATION - Regulatory Liabilities - SWEPCO (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 53.5	$ 26.5
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	8,344.0	8,182.4
Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	322.0	207.9
Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	8,022.0	7,974.5
Pays/paying a return | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 21.6	3.3
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	$ 176.0	103.1
Pays/paying a return | Pending final regulatory determination | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	176.0	103.1
Pays/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	5,526.4	5,823.1
Pays/paying a return | Approved for payment | Income Taxes, Net
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	1,622.1	2,179.7
Pays/paying a return | Approved for payment | Asset Removal Costs
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	3,828.0	3,563.5
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	40.4	35.0
Does not pay/paying a return | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 31.9	23.2
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	$ 146.0	104.8
Does not pay/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 2,495.6	2,151.4
Does not pay/paying a return | Approved for payment | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Remaining Refund Period	8 years
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	$ 32.1	26.1
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	90.1	106.5
SOUTHWESTERN ELECTRIC POWER COMPANY
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	21.6	3.3
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	610.8	756.1
SOUTHWESTERN ELECTRIC POWER COMPANY | Pending final regulatory determination
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	7.0	7.0
SOUTHWESTERN ELECTRIC POWER COMPANY | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	603.8	749.1
SOUTHWESTERN ELECTRIC POWER COMPANY | Pays/paying a return | Over-recovered Fuel Costs
Regulatory Liability [Line Items]
Total Current Regulatory Liabilities	$ 21.6	3.3
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	$ 7.0	7.0
SOUTHWESTERN ELECTRIC POWER COMPANY | Pays/paying a return | Approved for payment
Regulatory Liability [Line Items]
Total Noncurrent Regulatory Liabilities and Deferred Investment Tax Credits	591.4	740.0
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	127.5	292.4
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	456.6	443.2
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	7.3	4.4
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	12.4	9.1
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	$ 12.4	$ 9.1