Derivative Instruments and Hedging Activities - Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023
Fair Value of Assets
Gross amount recognized	$ 15	$ 56
Gross amount eligible for offsetting	(14)	(19)
Net amount	1	37
Fair Value of Liabilities
Gross amount recognized	3,469	3,280
Gross amount eligible for offsetting	(14)	(19)
Net amount	$ 3,455	$ 3,261