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Debt and Other Obligations Debt and Other Obligations - Maturities Due (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Debt Instrument
2017	$ 1,617
2018	1,745
2019	1,091
2020	70
2021	1,901
Thereafter	17,665
Total	24,089
Short-term debt, net of discounts	1,407	$ 1,034	$ 596
Short-term debt, net of discounts total	1,407
Foreign currency exchange loss	150	$ 21
Net discount on sale of Bonds	100
Power bonds
Debt Instrument
Debt issuance costs	62
Other long-term debt
Debt Instrument
Debt issuance costs	$ 12