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Summary of Significant Accounting Policies General and Basis of Presentation (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2022 USD ($) People | Mar. 31, 2021 USD ($) | Mar. 31, 2022 USD ($) People | Mar. 31, 2021 USD ($) | Sep. 30, 2021 USD ($)
Accounting Policies [Abstract] |  |  |  |  |
Population of TVA's service area | People | 10 |  | 10 |  |
Appropriation-investment power program |  |  |  |  | $ 1,000
Depreciation expense | $ 455 | $ 346 | $ 908 | $ 691 |

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- Definition The remaining appropriation investment if no additional appropriations from Congress are received. + References No definition available. + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585 + Details
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