Debt and Other Obligations Debt and Other Obligations - Maturities Due (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Debt Instrument
2018	$ 1,370
2019	1,020
2020	1,272
2021	220
2022	2,262
Thereafter	15,913
Total	22,057
Short-Term Debt	0	$ 1,167
Net discount on sale of Bonds	113
Foreign Currency Transaction Gain (Loss), Unrealized	59	$ 62
Power bonds
Debt Instrument
Debt issuance costs	$ 54