Fair Value Measurements - Summary of Investment Income, Net Gains and Losses, Funds Restricted for Specific Transactions and Disbursements Related to Investments (Details) - USD ($) $ in Millions		12 Months Ended
		Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Fair Value Disclosures [Abstract]
Investment income	[1]	$ 15	$ 13	$ 16
Net gains (losses)	[1]	60	29	(102)
Funds restricted for specific transactions		5	9	74
Disbursements		$ (79)	$ (58)	$ (35)

[1] Included in the net interest and other expense (income) caption within the Statements of Consolidated Comprehensive Income (Loss).