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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, 2019	Sep. 30, 2020	Sep. 30, 2026	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2018
Debt Instrument
2018		$ 1,901
2019		1,071
2020		69
2021		1,058
2022		1,059
Thereafter		15,957
Total		21,115
Short-term debt, net of discounts	$ 922	57	$ 0	$ 0	$ 0	$ 0	$ 0	$ 1,217
Short-term debt, net of discounts total		57
Foreign Currency Transaction Gain (Loss), before Tax	$ 191	80
Net discount on sale of Bonds		77
Foreign Currency Transaction Gain (Loss), Unrealized		153
Power bonds
Debt Instrument
Debt issuance costs		45
Other long-term debt
Debt Instrument
Debt issuance costs		$ 8