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Fair Value Measurements Fair Value Measurements - Investments (Details) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2023 USD ($) Units	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) Units	Jun. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)
Investment Gains (Losses)
Financing Receivable, after Allowance for Credit Loss	$ 127		$ 127		$ 96
Balance in NDT	$ 2,900		$ 2,900
Period of time where the investor contributes capital to an investment in a private partnership - minimum | Units	3		3
Period of time where the investor contributes capital to an investment in a private partnership - maximum | Units	4		4
Minimum investment period | Units	10		10
Number of readily available quoted exchange prices for the investments	0		0
Investment funds	$ 4,202		$ 4,202		3,671
Affiliated Entity
Investment Gains (Losses)
Investment funds	302		302		$ 358
LTDCP [Member]
Investment Gains (Losses)
Unrealized gains (losses) on investments	(1)	$ 2	(2)	$ 4
SERP
Investment Gains (Losses)
Unrealized gains (losses) on investments	(2)	9	(9)	14
ART [Member]
Investment Gains (Losses)
Unrealized gains (losses) on investments	(24)	139	(145)	147
NDT [Member]
Investment Gains (Losses)
Unrealized gains (losses) on investments	(51)	$ 331	292	$ 305
Equity Funds
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	210		210
Real Estate Funds
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	123		123
Credit [Member]
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	64		64
Private Equity Funds [Member]
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	116		116
Private real estate funds [Member]
Investment Gains (Losses)
Fair value plan assets gross	61		61
Private Credit [Member]
Investment Gains (Losses)
NDT unfunded commitments related to private equity and real estate	$ 34		$ 34

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- References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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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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The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning nuclear facilities.

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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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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

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Amortized cost, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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