Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2015	Sep. 30, 2014
Regulatory Assets and Liabilities
Current regulatory assets	$ 549	$ 481
Non-current regulatory assets	8,787	8,994
Regulatory assets	9,336	9,475
Current regulatory liabilities	168	184
Non-current regulatory liabilities	1	0
Regulatory liabilities	169	184
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	165	182
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory liabilities	3	2
Non-current regulatory liabilities	1	0
Deferred nuclear generating units
Regulatory Assets and Liabilities
Current regulatory assets	236	237
Non-current regulatory assets	1,097	1,255
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets	182	134
Non-current regulatory assets	81	72
Environmental agreements
Regulatory Assets and Liabilities
Current regulatory assets	70	54
Non-current regulatory assets	63	108
Environmental cleanup costs - Kingston ash spill
Regulatory Assets and Liabilities
Current regulatory assets	45	47
Non-current regulatory assets	362	421
Fuel cost adjustment receivable/liability
Regulatory Assets and Liabilities
Current regulatory assets	14	9
Other current regulatory assets
Regulatory Assets and Liabilities
Current regulatory assets	2	0
Deferred pension costs and other post-retirement benefits costs
Regulatory Assets and Liabilities
Non-current regulatory assets	4,087	4,297
Deferred pension costs due to actions of regulator
Regulatory Assets and Liabilities
Non-current regulatory assets	171	0
Unrealized losses on interest rate derivatives
Regulatory Assets and Liabilities
Non-current regulatory assets	1,028	957
Nuclear decommissioning costs
Regulatory Assets and Liabilities
Non-current regulatory assets	892	931
Non-nuclear decommissioning costs
Regulatory Assets and Liabilities
Non-current regulatory assets	720	645
Other non-current regulatory assets
Regulatory Assets and Liabilities
Non-current regulatory assets	$ 286	$ 308

Regulatory Assets and Liabilities [Line Items]

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- Definition

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 Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 1

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

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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.

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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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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 Accounting Standards Codification

-Topic 980

-SubTopic 405

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

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

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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

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