Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019
Regulatory Assets and Liabilities
Current regulatory assets	$ 159	$ 156
Non-current regulatory assets	8,410	8,763
Regulatory assets	8,569	8,919
Current regulatory liabilities	137	150
Regulatory Liability, Noncurrent	1
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	134	138
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory liabilities	3	12
Non-nuclear decommissioning costs
Regulatory Assets and Liabilities
Current regulatory assets	89	89
Non-current regulatory assets	1,074	1,241
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets	49	39
Non-current regulatory assets	17	15
Fuel cost adjustment receivable/liability
Regulatory Assets and Liabilities
Current regulatory assets	21	28
Deferred pension costs and other post-retirement benefits costs
Regulatory Assets and Liabilities
Non-current regulatory assets	4,678	4,756
Nuclear decommissioning costs
Regulatory Assets and Liabilities
Non-current regulatory assets	765	868
Environmental agreements
Regulatory Assets and Liabilities
Non-current regulatory assets	1,725	1,741
Other non-current regulatory assets
Regulatory Assets and Liabilities
Non-current regulatory assets	$ 151	$ 142

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://fasb.org/us-gaap/role/ref/legacyRef
-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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- 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 current liability as itemized in a table of regulatory current liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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- 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://fasb.org/us-gaap/role/ref/legacyRef
-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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