Income Taxes Uncertain Tax Position, Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2015	Sep. 30, 2017	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2014
Income Tax Disclosure [Abstract]
Income Tax Examination, estimate of impact			$ 25
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities				$ 440
Unrecognized Tax Benefits, Decrease (Increase) Resulting from Tax Audit Resolution	$ 191	$ 99
Unrecognized Tax Benefits	2,173	1,052	2,173	1,052	$ 1,706	$ 1,493
Amount of unrecognized tax benefits which may impact effective tax rate	2,047	997	2,047	997	1,604
Total net accrued interest, net of tax benefit	$ 99	$ 33	$ 99	$ 33	$ 84