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Fair Value Measurements Fair Value Measurements (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Mar. 31, 2024 | Mar. 31, 2023 | Sep. 30, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |
Financing Receivable, after Allowance for Credit Loss |  | $ 101 |  | $ 101 |  | $ 96 |
Investments |  |  |  |  |  |  |
Government debt securities |  | 505 |  | 505 |  | 451 |
Corporate debt securities |  | 347 |  | 347 |  | 300 |
Mortgage and asset-backed securities |  | 45 |  | 45 |  | 36 |
Institutional mutual funds |  | 316 |  | 316 |  | 288 |
Forward debt securities contracts |  | 5 |  | 5 |  | 11 |
Private credit measured at net asset value |  | 192 |  | 192 |  | 158 |
Private equity funds measured at net asset value(1) |  | 691 |  | 691 |  | 583 | [1]
Private real estate funds measured at net asset value(1) |  | 418 |  | 418 |  | 387 | [1]
Commingled funds measured at net asset value(1) |  | 1,273 |  | 1,273 |  | 1,156 | [1]
Total investments |  | 4,655 |  | 4,655 |  | 4,123 |
Commodity contract derivatives |  | 18 |  | 18 |  | 33 |
Total |  | 4,674 |  | 4,674 |  | 4,160 |
Liabilities |  |  |  |  |  |  |
Currency swaps | [2] | 125 |  | 125 |  | 141 |
Interest rate swaps |  | 753 |  | 753 |  | 662 |
Commodity contract derivatives |  | 4 |  | 4 |  | 2 |
Total |  | 1,149 |  | 1,149 |  | 991 |
Equity Securities, FV-NI |  | 686 |  | 686 |  | 608 |
Cash, Cash Equivalents, and Short-Term Investments |  | 177 |  | 177 |  | 145 |
Interest Rate Derivative Assets, at Fair Value |  | 1 |  | 1 |  | 4 |
Government debt securities reclassed |  |  |  |  |  | 104 |
Commingled funds reclassed |  |  |  |  |  | 21 |
Commodity Contract under FHP |  |  |  |  |  |  |
Liabilities |  |  |  |  |  |  |
Derivative Liability, Not Subject to Master Netting Arrangement |  | 267 |  | 267 |  | 186 |
NDT [Member] |  |  |  |  |  |  |
Liabilities |  |  |  |  |  |  |
Debt and Equity Securities, Unrealized Gain (Loss) |  | 24 | $ 34 | 70 | $ 60 |  |
Debt and Equity Securities, Unrealized Gain (Loss) |  | 24 | 34 | 70 | 60 |  |
ART [Member] |  |  |  |  |  |  |
Liabilities |  |  |  |  |  |  |
Debt and Equity Securities, Unrealized Gain (Loss) |  | 8 | 8 | 24 | 18 |  |
Debt and Equity Securities, Unrealized Gain (Loss) |  | 8 | $ 8 | 24 | $ 18 |  |
RP |  |  |  |  |  |  |
Liabilities |  |  |  |  |  |  |
Debt and Equity Securities, Unrealized Gain (Loss) |  |  |  | 1 |  |  |
Debt and Equity Securities, Unrealized Gain (Loss) |  |  |  | 1 |  |  |
Fair Value, Inputs, Level 1 |  |  |  |  |  |  |
Investments |  |  |  |  |  |  |
Government debt securities |  | 440 |  | 440 |  | 391 |
Corporate debt securities |  | 0 |  | 0 |  | 0 |
Mortgage and asset-backed securities |  | 0 |  | 0 |  | 0 |
Institutional mutual funds |  | 316 |  | 316 |  | 288 |
Forward debt securities contracts |  | 0 |  | 0 |  | 0 |
Private credit measured at net asset value |  | 0 |  | 0 |  | 0 |
Private equity funds measured at net asset value(1) |  | 0 |  | 0 |  | 0 | [1]
Private real estate funds measured at net asset value(1) |  | 0 |  | 0 |  | 0 | [1]
Commingled funds measured at net asset value(1) |  | 0 |  | 0 |  | 0 | [1]
Total investments |  | 1,442 |  | 1,442 |  | 1,287 |
Commodity contract derivatives |  | 0 |  | 0 |  | 0 |
Total |  | 1,442 |  | 1,442 |  | 1,287 |
Liabilities |  |  |  |  |  |  |
Currency swaps |  | 0 |  | 0 |  | 0 | [2]
Interest rate swaps |  | 0 |  | 0 |  | 0 |
Commodity contract derivatives |  | 0 |  | 0 |  | 0 |
Total |  | 0 |  | 0 |  | 0 |
Equity Securities, FV-NI |  | 686 |  | 686 |  | 608 |
Cash, Cash Equivalents, and Short-Term Investments |  | 0 |  | 0 |  | 0 |
Interest Rate Derivative Assets, at Fair Value |  | 0 |  | 0 |  | 0 |
Fair Value, Inputs, Level 1 | Commodity Contract under FHP |  |  |  |  |  |  |
Liabilities |  |  |  |  |  |  |
Derivative Liability, Not Subject to Master Netting Arrangement |  | 0 |  | 0 |  | 0 |
Fair Value, Inputs, Level 2 |  |  |  |  |  |  |
Investments |  |  |  |  |  |  |
Government debt securities |  | 65 |  | 65 |  | 60 |
Corporate debt securities |  | 347 |  | 347 |  | 300 |
Mortgage and asset-backed securities |  | 45 |  | 45 |  | 36 |
Institutional mutual funds |  | 0 |  | 0 |  | 0 |
Forward debt securities contracts |  | 5 |  | 5 |  | 11 |
Private credit measured at net asset value |  | 0 |  | 0 |  | 0 |
Private equity funds measured at net asset value(1) |  | 0 |  | 0 |  | 0 | [1]
Private real estate funds measured at net asset value(1) |  | 0 |  | 0 |  | 0 | [1]
Commingled funds measured at net asset value(1) |  | 0 |  | 0 |  | 0 | [1]
Total investments |  | 639 |  | 639 |  | 552 |
Commodity contract derivatives |  | 18 |  | 18 |  | 33 |
Total |  | 658 |  | 658 |  | 589 |
Liabilities |  |  |  |  |  |  |
Currency swaps |  | 125 |  | 125 |  | 141 | [2]
Interest rate swaps |  | 753 |  | 753 |  | 662 |
Commodity contract derivatives |  | 4 |  | 4 |  | 2 |
Total |  | 1,149 |  | 1,149 |  | 991 |
Equity Securities, FV-NI |  | 0 |  | 0 |  | 0 |
Cash, Cash Equivalents, and Short-Term Investments |  | 177 |  | 177 |  | 145 |
Interest Rate Derivative Assets, at Fair Value |  | 1 |  | 1 |  | 4 |
Fair Value, Inputs, Level 2 | Commodity Contract under FHP |  |  |  |  |  |  |
Liabilities |  |  |  |  |  |  |
Derivative Liability, Not Subject to Master Netting Arrangement |  | 267 |  | 267 |  | 186 |
Fair Value, Inputs, Level 3 |  |  |  |  |  |  |
Investments |  |  |  |  |  |  |
Government debt securities |  | 0 |  | 0 |  | 0 |
Corporate debt securities |  | 0 |  | 0 |  | 0 |
Mortgage and asset-backed securities |  | 0 |  | 0 |  | 0 |
Institutional mutual funds |  | 0 |  | 0 |  | 0 |
Forward debt securities contracts |  | 0 |  | 0 |  | 0 |
Private credit measured at net asset value |  | 0 |  | 0 |  | 0 |
Private equity funds measured at net asset value(1) |  | 0 |  | 0 |  | 0 | [1]
Private real estate funds measured at net asset value(1) |  | 0 |  | 0 |  | 0 | [1]
Commingled funds measured at net asset value(1) |  | 0 |  | 0 |  | 0 | [1]
Total investments |  | 0 |  | 0 |  | 0 |
Commodity contract derivatives |  | 0 |  | 0 |  | 0 |
Total |  | 0 |  | 0 |  | 0 |
Liabilities |  |  |  |  |  |  |
Currency swaps |  | 0 |  | 0 |  | 0 | [2]
Interest rate swaps |  | 0 |  | 0 |  | 0 |
Commodity contract derivatives |  | 0 |  | 0 |  | 0 |
Total |  | 0 |  | 0 |  | 0 |
Equity Securities, FV-NI |  | 0 |  | 0 |  | 0 |
Cash, Cash Equivalents, and Short-Term Investments |  | 0 |  | 0 |  | 0 |
Interest Rate Derivative Assets, at Fair Value |  | 0 |  | 0 |  | 0 |
Fair Value, Inputs, Level 3 | Commodity Contract under FHP |  |  |  |  |  |  |
Liabilities |  |  |  |  |  |  |
Derivative Liability, Not Subject to Master Netting Arrangement |  | $ 0 |  | $ 0 |  | $ 0 |
[1] | Certain investments that are measured at fair value using the NAV or its equivalent (alternative investments) have not been categorized in the fair value hierarchy. The inputs to these fair value measurements include underlying NAVs, discounted cash flow valuations, comparable market valuations, and adjustments for currency, credit, liquidity, and other risks. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the amounts presented on the Consolidated Balance Sheets. (4) TVA records currency swaps net of cash collateral received from or paid to the counterparty if applicable, to the extent such amount is not recorded in Accounts payable and accrued liabilities. See Note 13 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities.
[2] | TVA records currency swaps net of cash collateral received from or paid to the counterparty if applicable, to the extent such amount is not recorded in Accounts payable and accrued liabilities. See Note 13 — Risk Management Activities and Derivative Transactions — Offsetting of Derivative Assets and Liabilities.

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- Definition Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(9)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 + Details
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- Definition The fair value as of the balance sheet date of firm holdings in debt obligations issued by the US government including short-term Treasury bills, medium-term Treasury notes, and long-term Treasury bonds, as well as debt issued by agencies. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481961/940-320-45-2 + Details
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