The population of the company's service area.

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[Line Items] for Reclassification of Amounts on Cash Flow and Statement of Operations [Table]

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The remaining appropriation investment if no additional appropriations from Congress are received.

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Amount of allowance for credit loss on accounts receivable, classified as current.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

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Net amount of other deferred costs capitalized at the end of the reporting period. Does not include deferred finance costs or deferred acquisition costs of insurance companies.

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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.

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Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Summary of Significant Accounting Policies General and Basis of Presentation (Details) People in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2019 USD ($) People	Dec. 31, 2017 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)
Reclassification of Amounts on Cash Flow and Statement of Operations [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 304		$ 299
Restricted Cash and Cash Equivalents	23		23
Regulatory Assets	8,569		8,919
Other Deferred Costs, Net	(10)
Appropriation-investment power program			1,000
Financing Receivable, after Allowance for Credit Loss	$ 124		120
Population of TVA's service area \| People	10
Allowance for uncollectible accounts	$ 1		1
Depreciation expense	539	$ 308
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 327		$ 322	$ 322	$ 324