Regulatory Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Sep. 30, 2011
Regulatory Assets and Liabilities
Current regulatory assets	$ 854	$ 543
Non-current regulatory assets	11,403	11,505
Regulatory assets	12,257	12,048
Current regulatory liabilities	168	280
Non-current regulatory liabilities	113	285
Regulatory liabilities	281	565
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	155	127
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory liabilities	13	153
Non-current regulatory liabilities	113	285
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets	441	225
Non-current regulatory assets	446	221
Deferred nuclear generating units
Regulatory Assets and Liabilities
Current regulatory assets	236	236
Non-current regulatory assets	532	709
Environmental agreements
Regulatory Assets and Liabilities
Current regulatory assets	87	0
Non-current regulatory assets	251	346
Environmental cleanup costs - Kingston ash spill
Regulatory Assets and Liabilities
Current regulatory assets	70	73
Non-current regulatory assets	817	874
Fuel cost adjustment receivable
Regulatory Assets and Liabilities
Current regulatory assets	19	7
Deferred capital leases
Regulatory Assets and Liabilities
Current regulatory assets	1	2
Deferred pension costs and other post-retirement benefits costs
Regulatory Assets and Liabilities
Non-current regulatory assets	5,537	5,807
Unrealized losses on swaps and swaptions
Regulatory Assets and Liabilities
Non-current regulatory assets	1,350	1,164
Nuclear decommissioning costs
Regulatory Assets and Liabilities
Non-current regulatory assets	942	1,012
Construction costs
Regulatory Assets and Liabilities
Non-current regulatory assets	619	619
Non-nuclear decommissioning costs
Regulatory Assets and Liabilities
Non-current regulatory assets	548	519
Other non-current regulatory assets
Regulatory Assets and Liabilities
Non-current regulatory assets	$ 361	$ 234

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 9, 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

+ Details

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- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

+ References

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

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- Definition

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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- Definition

The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

+ Details

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- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.24)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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