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Debt and Other Obligations Debt and Other Obligations - Maturities Due (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Debt Instrument
2018	$ 1,028
2019	29
2020	1,022
2021	1,022
2022	1,370
Thereafter	14,187
Total	18,658
Short-term debt, net of discounts	780	$ 57
Short-term debt, net of discounts total	780
Foreign Currency Transaction Gain (Loss), before Tax	58	$ 80
Net discount on sale of Bonds	72
Foreign Currency Transaction Gain (Loss), Unrealized	58
Scenario, Forecast
Debt Instrument
Short-term debt, net of discounts			$ 0	$ 0	$ 0	$ 0	$ 0
Power bonds
Debt Instrument
Debt issuance costs	43
Other long-term debt
Debt Instrument
Debt issuance costs	$ 7