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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

X

- 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.

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Fair value portion of arrangements with third parties, including, but not limited to, operating lease arrangement and arrangement in which the entity has agreed to expend funds to procure goods or services, or has agreed to commit resources to supply goods or services.

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Amount of unrealized gain (loss) on investment in debt and equity securities.

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