Commitments, Guarantees and Contingencies (Details) (USD $)	3 Months Ended
	Mar. 31, 2012
Letters of Credit [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Credit Facilities, Total	$ 3,250,000,000
Letters of Credit Limit	1,350,000,000
Maximum Future Payments for Letters of Credit	189,000,000
Variable Rate PCBs Supported	402,000,000
Bilateral Letters of Credit	407,000,000
Master Lease Agreements [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Maximum Potential Loss on Master Lease Agreements	15,000,000
Guaranteed Sales Proceeds Percentage of Fair Value to Lessor Current Term	84.00%
Guaranteed Sales Proceeds Percentage of Fair Value to Lessor End of Max Lease Term	77.00%
Indiana Michigan Power Co [Member] | Master Lease Agreements [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Future Minimum Lease Obligation for Remaining Railcars	16,000,000
Maximum Potential Loss on Guarantee of Return-and-Sale Option	12,000,000
Southwestern Electric Power Co [Member] | Master Lease Agreements [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Future Minimum Lease Obligation for Remaining Railcars	18,000,000
Maximum Potential Loss on Guarantee of Return-and-Sale Option	13,000,000
Southwestern Electric Power Co [Member] | Guarantees of Third Party Obligations [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Guarantees of Mine Reclamation, Amount	100,000,000
Estimated Final Cost Mine Reclamation	58,000,000
Total Amount Collected through a Rider for Final Mine Closure and Reclamation Costs	54,000,000
Amount Collected through a Rider for Final Mine Closure - Other Current Liabilities	16,000,000
Amount Collected through a Rider for Final Mine Closure - ARO Noncurrent	38,000,000
Superfund and State Remediation [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Expense Recorded Due to Remediation Work Remaining Provision	10,000,000
Cook Plant Unit 1 Fire and Shutdown [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Estimated Repair of the Property Damage and Rotor Replacement Cost	400,000,000
Recoverable Amount Under the Property Insurance Policy	64,000,000
Received Partial Payments for the Cost Incurred to Repair Property Damage	203,000,000
Insurance Recovery Recorded in Revenues During the Outage Period	185,000,000
Alaskan Villages Claim [Member] | From [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Amount Required for Relocation of the Village	95,000,000
Alaskan Villages Claim [Member] | To [Member]
Commitments, Guarantees and Contingencies (Textuals) [Abstract]
Amount Required for Relocation of the Village	$ 400,000,000