Gallatin Coal Combustion Residual Facilities (Details) - USD ($)	6 Months Ended
Mar. 31, 2019	Sep. 30, 2018
Other Long-Term Liabilities
Current regulatory assets	$ 241,000,000	$ 414,000,000
Gallatin coal combustion residual facilities original estimated cost for dewatering facility	71,000,000
Gallatin coal combustion residual facilities estimated cost relocate offsite	2,000,000,000
TDEC civil penalties related to Gallatin	17,000
Plaintiff civil penalties related to Gallatin	37,500
Gallatin coal combustion residual facilities estimated cost relocate onsite	900,000,000
Other long-term liabilities
Other Long-Term Liabilities
Gallatin coal combustion residual facilities	864,000,000	$ 862,000,000
Accounts payable and accrued liabilities
Other Long-Term Liabilities
Gallatin coal combustion residual facilities	$ 22,000,000

Gallatin coal combustion residual facilities estimated cost relocate offsite

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Gallatin coal combustion residual facilities estimated cost to relocate onsite

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Gallatin coal combustion residual facilities original estimated cost for dewatering facility

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Other Long-Term Liabilities [Line Items]

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The amount per day the plaintiffs in the Gallatin Fossil Plant CCR cases are seeking for violations related to the TN Water Quality Control Act and TN Solid Waste Disposal Act.

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The amount per day TDEC is seeking for each day TVA is found to have violated the statutes related to the TN Water Quality Control Act and TN Solid Waste Disposal Act in relation to Gallatin Fossil Plant.

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Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable after twelve months or beyond the next operating cycle if longer.

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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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