Derivative Instruments and Hedging Activities Derivative Assets and Liabilties, Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross amount recognized, derivative assets	$ 80	$ 91
Gross amount eligible for offsetting, derivative assets	(12)	(16)
Net amount, derivative assets	68	75
Gross amount, derivative liabilities	3,175	2,105
Gross amount eligible for offsetting, derivative liabilities	(12)	(16)
Net Amount, derivative liabilities	$ 3,163	$ 2,089