Subsequent Events (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($) MW	Oct. 28, 2021 USD ($)
Mitchell Power Plant
Generation MWs | MW	1,560
Accounts Receivable and Accrued Unbilled Revenues [Member]
Major Classes of Assets	$ 24.7
Fuel, Materials and Supplies [Member]
Major Classes of Assets	26.5
Property, Plant and Equipment
Major Classes of Assets	2,264.6
Other Regulatory Assets (Liabilities) [Member]
Major Classes of Assets	501.7
Other Classes of Assets that are not Major [Member]
Major Classes of Assets	43.8
Total Assets [Member]
Major Classes of Assets	2,861.3
Accounts Payable [Member]
Major Classes of Liabilities	51.2
Long-term Debt Due Within One Year [Member]
Major Classes of Liabilities	125.0
Customer Deposits [Member]
Major Classes of Liabilities	31.9
Deferred Income Taxes [Member]
Major Classes of Liabilities	448.3
Long-term Debt [Member]
Major Classes of Liabilities	978.0
Regulatory Liabilities and Deferred Investment Tax Credits [Member]
Major Classes of Liabilities	146.5
Other Classes of Liabilities that are not Major [Member]
Major Classes of Liabilities	93.2
Total Liabilities [Member]
Major Classes of Liabilities	1,874.1
AEP Transmission Co [Member] | Accounts Receivable and Accrued Unbilled Revenues [Member]
Major Classes of Assets	1.6
AEP Transmission Co [Member] | Fuel, Materials and Supplies [Member]
Major Classes of Assets	0.0
AEP Transmission Co [Member] | Property, Plant and Equipment
Major Classes of Assets	164.5
AEP Transmission Co [Member] | Other Regulatory Assets (Liabilities) [Member]
Major Classes of Assets	0.0
AEP Transmission Co [Member] | Other Classes of Assets that are not Major [Member]
Major Classes of Assets	0.3
AEP Transmission Co [Member] | Total Assets [Member]
Major Classes of Assets	166.4
AEP Transmission Co [Member] | Accounts Payable [Member]
Major Classes of Liabilities	1.5
AEP Transmission Co [Member] | Long-term Debt Due Within One Year [Member]
Major Classes of Liabilities	0.0
AEP Transmission Co [Member] | Customer Deposits [Member]
Major Classes of Liabilities	0.0
AEP Transmission Co [Member] | Deferred Income Taxes [Member]
Major Classes of Liabilities	14.9
AEP Transmission Co [Member] | Long-term Debt [Member]
Major Classes of Liabilities	0.0
AEP Transmission Co [Member] | Regulatory Liabilities and Deferred Investment Tax Credits [Member]
Major Classes of Liabilities	7.5
AEP Transmission Co [Member] | Other Classes of Liabilities that are not Major [Member]
Major Classes of Liabilities	4.2
AEP Transmission Co [Member] | Total Liabilities [Member]
Major Classes of Liabilities	$ 28.1
Kentucky Power Co [Member] | Mitchell Power Plant
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%
Wheeling Power Company | Mitchell Power Plant
Jointly Owned Utility Plant, Proportionate Ownership Share	50.00%
Subsequent Event [Member]
Cash expected for sale of asset		$ 1,450.0
Stock Purchase Agreement		$ 2,850.0