Income Taxes - Deferred Income Taxes (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Compensation and benefits, assets	$ 513	$ 458
Loss and credit carryforwards, assets	1,327	1,290
Other, assets	634	707
Deferred income taxes, assets, gross	2,474	2,455
Valuation allowance, assets	(1,240)	(1,181)
Deferred income taxes, assets	1,234	1,275
Property and equipment, liabilities	255	253
Deferred Tax Liabilities, Other Finite-Lived Assets	2,624	2,948
Other, liabilities	189	384
Deferred income taxes, liabilities, gross	3,068	3,585
Deferred income taxes, liabilities	$ 3,068	$ 3,585