Commitments and Contingencies (Commitments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Power Purchase Contracts
Commitments and Guarantees
Estimated additional commitments, 2014	$ 17
Estimated additional commitments, 2015	43
Estimated additional commitments, 2016	66
Estimated additional commitments, thereafter	970
Power Purchase Contracts \| Operating Leases
Commitments and Guarantees
Estimated additional commitments, 2015	21
Estimated additional commitments, 2016	45
Estimated additional commitments, thereafter	942
Environmental Indemnities
Commitments and Guarantees
Maximum liability under indemnity per Mountainview purchase agreement for damages and other amounts	$ 60

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The maximum aggregate potential liability under the purchase agreement for damages and other amounts in connection with environmental liabilities.

No definition available.

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Amount of the recorded unconditional purchase obligation maturing after the fifth rolling twelve months following the latest balance sheet presented.

No definition available.

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Amount of the recorded unconditional purchase obligation maturing in the fifth rolling twelve months following the latest balance sheet presented.

No definition available.

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Amount of the recorded unconditional purchase obligation maturing in the fourth rolling twelve months following the latest balance sheet presented.

No definition available.

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Amount of the recorded unconditional purchase obligation maturing in the third rolling twelve months following the latest balance sheet presented.

No definition available.

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