Commitments, Guarantees and Contingencies (Details) - Jun. 30, 2015 - USD ($) $ in Thousands	Total
Letters of Credit [Member]
Maximum Future Payments for Letters of Credit [Abstract]
Maximum Future Payments for Letters of Credit	$ 61,000
Pollution Control Bonds Supported by Bilateral Letters of Credit [Abstract]
Variable Rate PCBs Supported	477,000
Bilateral Letters of Credit	483,000
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Revolving Credit Facilities	3,500,000
Letters of Credit Limit	1,200,000
Maximum Future Payments for Letters of Credit	61,000
Uncommitted Facility	100,000
Maximum Future Payments for Letters of Credit Issued Under the Uncommitted Facility	100,000
Variable Rate PCBs Supported	477,000
Bilateral Letters of Credit	483,000
Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	30,000
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Max Potential Loss on Master Lease Agreements	30,000
Guarantees of Third Party Obligations [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Guarantees of Mine Reclamation, Amount	115,000
Estimated Final Cost Mine Reclamation	58,000
Total Amount Collected through a Rider for Final Mine Closure and Reclamation Costs	65,000
Amount Collected through a Rider for Final Mine Closure - Other Liabilities Noncurrent	16,000
Amount Collected through a Rider for Final Mine Closure - ARO Noncurrent	49,000
Indiana Michigan Power Co [Member] | Letters of Credit [Member]
Maximum Future Payments for Letters of Credit [Abstract]
Maximum Future Payments for Letters of Credit	35
Pollution Control Bonds Supported by Bilateral Letters of Credit [Abstract]
Variable Rate PCBs Supported	77,000
Bilateral Letters of Credit	77,886
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Maximum Future Payments for Letters of Credit	35
Variable Rate PCBs Supported	77,000
Bilateral Letters of Credit	77,886
Indiana Michigan Power Co [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	3,323
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Max Potential Loss on Master Lease Agreements	3,323
Future Minimum Lease Obligation for Remaining Railcars	$ 11,000
Guaranteed Sales Proceeds Percentage of Fair Value to Lessor Current Term	83.00%
Guaranteed Sales Proceeds Percentage of Fair Value to Lessor End of Max Lease Term	77.00%
Maximum Potential Loss on Guarantee of Return-and-Sale Option	$ 9,000
Southwestern Electric Power Co [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	2,825
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Max Potential Loss on Master Lease Agreements	2,825
Future Minimum Lease Obligation for Remaining Railcars	$ 12,000
Guaranteed Sales Proceeds Percentage of Fair Value to Lessor Current Term	83.00%
Guaranteed Sales Proceeds Percentage of Fair Value to Lessor End of Max Lease Term	77.00%
Maximum Potential Loss on Guarantee of Return-and-Sale Option	$ 10,000
Southwestern Electric Power Co [Member] | Guarantees of Third Party Obligations [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Guarantees of Mine Reclamation, Amount	115,000
Estimated Final Cost Mine Reclamation	58,000
Total Amount Collected through a Rider for Final Mine Closure and Reclamation Costs	65,000
Amount Collected through a Rider for Final Mine Closure - Other Liabilities Noncurrent	16,000
Amount Collected through a Rider for Final Mine Closure - ARO Noncurrent	49,000
Ohio Power Co [Member] | Letters of Credit [Member]
Maximum Future Payments for Letters of Credit [Abstract]
Maximum Future Payments for Letters of Credit	4,200
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Maximum Future Payments for Letters of Credit	4,200
Ohio Power Co [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	5,618
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Max Potential Loss on Master Lease Agreements	5,618
Appalachian Power Co [Member] | Letters of Credit [Member]
Pollution Control Bonds Supported by Bilateral Letters of Credit [Abstract]
Variable Rate PCBs Supported	229,650
Bilateral Letters of Credit	232,293
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Variable Rate PCBs Supported	229,650
Bilateral Letters of Credit	232,293
Appalachian Power Co [Member] | Master Lease Agreements [Member]
Maximum Potential Loss on Master Lease Agreements [Abstract]
Max Potential Loss on Master Lease Agreements	4,864
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Max Potential Loss on Master Lease Agreements	4,864
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	2,428
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Max Potential Loss on Master Lease Agreements	2,428
Superfund and State Remediation [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Expense Recorded Due to Remediation Work Remaining Provision	9,000
Superfund and State Remediation [Member] | Indiana Michigan Power Co [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Expense Recorded Due to Remediation Work Remaining Provision	$ 9,000