Derivative Instruments and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Sep. 30, 2021
Offsetting Derivative Assets and Liabilities [Abstract]
Derivative assets	$ 75	$ 57
Gross amount eligible for offsetting, derivative assets	(17)	(16)
Net derivative amount, derivative assets	58	41
Derivative liabilities	2,871	2,936
Gross amount eligible for offsetting, derivative liabilities	(17)	(16)
Net derivative amount, derivative liabilities	$ 2,854	$ 2,920