Derivative Instruments and Hedging Activities Derivative Assets and Liabilties, Offsetting (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Gross amount recognized, derivative assets	$ 57	$ 87
Gross amount eligible for offsetting, derivative assets	(16)	(10)
Net amount, derivative assets	41	77
Gross amount, derivative liabilities	2,936	3,020
Gross amount eligible for offsetting, derivative liabilities	(16)	(10)
Net Amount, derivative liabilities	$ 2,920	$ 3,010