Derivative Instruments and Hedging Activities Derivative Assets and Liabilties, Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross amount recognized, derivative assets	$ 87	$ 97
Gross amount eligible for offsetting, derivative assets	(10)	(11)
Net amount, derivative assets	77	86
Gross amount, derivative liabilities	3,020	2,568
Gross amount eligible for offsetting, derivative liabilities	(10)	(11)
Net Amount, derivative liabilities	$ 3,010	$ 2,557