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		3 Months Ended		6 Months Ended
		Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Fair Value Disclosures [Abstract]
Investment income	[1]	$ 3	$ 2	$ 6	$ 10
Net gains (losses)	[1]	19	(28)	41	(24)
Funds restricted for specific transactions		0	44	5	44
Disbursements		$ (16)	$ (21)	$ (16)	$ (28)

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