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Debt and Other Obligations Debt and Other Obligations - Maturities Due (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2017
Debt Instrument
2018		$ 1,092
2019		1,901
2020		1,071
2021		69
2022		1,057
Thereafter		16,415
Total		21,605
Short-term debt, net of discounts	$ 1,216	922	$ 1,999
Short-term debt, net of discounts total		922
Foreign Currency Transaction Gain (Loss), before Tax	$ 147	191
Net discount on sale of Bonds		81
Power bonds
Debt Instrument
Debt issuance costs		50
Other long-term debt
Debt Instrument
Debt issuance costs		$ 8