Risk Management Activities and Derivative Transactions Fair Values of TVA Derivatives (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Derivatives, Fair Value
Forward Contract Derivative Asset, at Fair Value	$ 11	$ 22
Gross amounts of recognized liabilities	2,372	1,972
200 million Sterling currency swap
Derivatives, Fair Value
Fair value	(90)	(90)
Gross amounts of recognized liabilities	264	208
200 million Sterling currency swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(1)	(84)
200 million Sterling currency swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(89)	(6)
250 million Sterling currency swap
Derivatives, Fair Value
Fair value	(85)	(61)
250 million Sterling currency swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(79)	(56)
250 million Sterling currency swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(6)	(5)
150 million Sterling currency swap
Derivatives, Fair Value
Fair value	(89)	(57)
150 million Sterling currency swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(86)	(53)
150 million Sterling currency swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(3)	(4)
$1.0 billion notional interest rate swap
Derivatives, Fair Value
Fair value	(1,492)	(1,261)
$1.0 billion notional interest rate swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(1,415)	(1,199)
$1.0 billion notional interest rate swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(77)	(62)
$476 million notional interest rate swap
Derivatives, Fair Value
Fair value	(611)	(498)
$476 million notional interest rate swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(579)	(474)
$476 million notional interest rate swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(32)	(24)
$42 million notional interest rate swap
Derivatives, Fair Value
Fair value	(5)	(5)
$42 million notional interest rate swap \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(3)	(3)
$42 million notional interest rate swap \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(2)	(2)
Commodity contract derivatives
Derivatives, Fair Value
Fair value	(30)	(41)
Commodity contract derivatives \| Other long-term assets
Derivatives, Fair Value
Fair value	5	0
Commodity contract derivatives \| Other current assets
Derivatives, Fair Value
Fair value	5	12
Commodity contract derivatives \| Other long-term liabilities
Derivatives, Fair Value
Fair value	(2)	(16)
Commodity contract derivatives \| Accounts payable and accrued liabilities
Derivatives, Fair Value
Fair value	(38)	(37)
Fair Value, Inputs, Level 2
Derivatives, Fair Value
Forward Contract Derivative Asset, at Fair Value	$ 11	$ 22

Fair value as of the balance sheet date of forward contract derivative assets.

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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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