Commitments, Guarantees and Contingencies (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Oct. 25, 2018
Letters of Credit [Member]
Maximum Future Payments for Letters of Credit [Abstract]
Maximum Future Payments for Letters of Credit Issued Under the Uncommitted Facility	$ 71.8
Pollution Control Bonds Supported by Bilateral Letters of Credit [Abstract]
Variable Rate PCBs Supported	45.0
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Letters of Credit Limit	1,200.0
Uncommitted Facility	305.0
Guarantees of Third Party Obligations [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Guarantees of Mine Reclamation, Amount	140.0
Estimated Final Cost Mine Reclamation	79.0
Total Amount Collected through a Rider for Final Mine Closure and Reclamation Costs	74.0
Amount Collected through a Rider for Final Mine Closure - ARO Noncurrent	79.0
Amount Collected, Rider Mine Close Other Assets Noncurrent	5.0
Guarantees of Equity Method Investees [Member]
Maximum Potential Amount of Future Payments Associated with Guarantee	75.0
Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	47.7
Boat and Barge Leases [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Maximum Potential Lease Payments, AEPRO Barge and Boat Leases	46.0
Guarantee Liability related to AEPRO Boat and Barge Leases	6.0
Guarantee Liability related to AEPRO Boat and Barge Leases - Other Current Liabilities	1.0
Guarantee Liability related to AEPRO Boat and Barge Leases - Other Noncurrent Liabilities	5.0
AEP Texas Inc. [Member] | Letters of Credit [Member]
Maximum Future Payments for Letters of Credit [Abstract]
Maximum Future Payments for Letters of Credit Issued Under the Uncommitted Facility	2.8
AEP Texas Inc. [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	11.4
Appalachian Power Co [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	8.8
Indiana Michigan Power Co [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	3.5
Indiana Michigan Power Co [Member] | Railcar Lease [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Future Minimum Lease Obligations for Remaining Railcars	$ 7.0
Guaranteed Sales Proceeds Percentage of Fair Value to Lessor End of Max Lease Term	77.00%
Maximum Potential Loss on Guarantee	$ 5.0
Ohio Power Co [Member] | Letters of Credit [Member]
Maximum Future Payments for Letters of Credit [Abstract]
Maximum Future Payments for Letters of Credit Issued Under the Uncommitted Facility	0.6
Ohio Power Co [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	7.6
Public Service Co Of Oklahoma [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	4.1
Southwestern Electric Power Co [Member] | Guarantees of Third Party Obligations [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Guarantees of Mine Reclamation, Amount	140.0
Estimated Final Cost Mine Reclamation	79.0
Total Amount Collected through a Rider for Final Mine Closure and Reclamation Costs	74.0
Amount Collected through a Rider for Final Mine Closure - ARO Noncurrent	79.0
Amount Collected, Rider Mine Close Other Assets Noncurrent	5.0
Southwestern Electric Power Co [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	4.2
Southwestern Electric Power Co [Member] | Railcar Lease [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Future Minimum Lease Obligations for Remaining Railcars	$ 7.0
Guaranteed Sales Proceeds Percentage of Fair Value to Lessor End of Max Lease Term	77.00%
Maximum Potential Loss on Guarantee	$ 5.0
July 2019 [Member] | Letters of Credit [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Bilateral Letters of Credit, Matured	46.0
June 2021 [Member] | Letters of Credit [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Revolving Credit Facilities	$ 3,000.0
Subsequent Event [Member] | June 2022 [Member] | Letters of Credit [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Revolving Credit Facilities		$ 4,000.0