Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015
Offsetting Derivative Assets and Liabilities [Abstract]
Gross amount recognized, derivative assets	$ 193	$ 233	$ 258
Gross amount recognized, derivative liabilities	1,260	1,727	1,708
Gross amount eligible for offsetting, derivative assets	(18)	(8)	(8)
Gross amount eligible for offsetting, derivative liabilities	(18)	(8)	(8)
Net derivative amount, derivative assets	175	225	250
Net derivative amount, derivative liabilities	$ 1,242	$ 1,719	$ 1,700