Income Taxes - Deferred Income Taxes (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Compensation and benefits, assets	$ 527	$ 554
Loss and credit carryforwards, assets	2,107	1,900
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Reserves	191	241
Other, assets	555	501
Deferred income taxes, assets, gross	3,379	3,196
Valuation allowance, assets	(2,036)	(1,820)
Deferred income taxes, assets	1,343	1,376
Property and equipment, liabilities	410	361
Deferred Tax Liabilities, Other Finite-Lived Assets	2,160	2,408
Other, liabilities	123	137
Deferred income taxes, liabilities, gross	2,693	2,906
Deferred income taxes, liabilities	$ 2,693	$ 2,906