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Fair Value Measurements - Investments (Details) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2024 USD ($) Units | Sep. 30, 2023 USD ($)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Long-term Investments | $ 4,968 | $ 4,123
Period of time where the investor contributes capital to an investment in a private partnership - minimum | Units | 3 |
Period of time where the investor contributes capital to an investment in a private partnership - maximum | Units | 4 |
Minimum investment period | 10 years |
Fair value of gross plan assets | $ 8,959 | 8,605
Number of readily available quoted exchange prices for the investments | 0 |
NDT |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Long-term Investments | $ 3,300 |
ART |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Long-term Investments | 1,500 |
LTDCP |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Unrealized gains (losses) on investments | 2 | 1
SERP |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Unrealized gains (losses) on investments | 14 | 6
ART |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Unrealized gains (losses) on investments | 171 | 96
Debt and Equity Securities, Unrealized Gain (Loss) | 36 | 13
NDT |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Unrealized gains (losses) on investments | 324 | 162
Debt and Equity Securities, Unrealized Gain (Loss) | 93 | 27
Equity Funds [Member] | NDT |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Commitments, Fair Value Disclosure | 382 |
Real Estate Funds [Member] | NDT |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Commitments, Fair Value Disclosure | 120 |
Credit [Member] | NDT |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Commitments, Fair Value Disclosure | 87 |
Defensive growth assets | ART |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Commitments, Fair Value Disclosure | 152 |
Private real estate funds | ART |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Commitments, Fair Value Disclosure | 61 |
Private Credit [Member] | ART |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Commitments, Fair Value Disclosure | 46 |
RP |  |
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items] |  |
Debt and Equity Securities, Unrealized Gain (Loss) | $ 1 | $ 1

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- Definition Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. This amount is not reduced by non-benefit liabilities. + References No definition available. + Details
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