Derivative Instruments and Hedging Activities Derivative Assets and Liabilties, Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross amount recognized, derivative assets	$ 91	$ 95
Gross amount eligible for offsetting, derivative assets	(16)	(21)
Net amount, derivative assets	75	74
Gross amount, derivative liabilities	2,105	2,980
Gross amount eligible for offsetting, derivative liabilities	(16)	(21)
Net Amount, derivative liabilities	$ 2,089	$ 2,959