Income Taxes - Deferred Income Taxes (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Compensation and benefits, assets	$ 458	$ 618
Loss and credit carryforwards, assets	1,290	1,098
Other, assets	707	531
Deferred income taxes, assets, gross	2,455	2,247
Valuation allowance, assets	(1,181)	(1,032)
Deferred income taxes, assets	1,275	1,216
Property and equipment, liabilities	253	244
Deferred Tax Liabilities, Other Finite-Lived Assets	2,948	1,584
Other, liabilities	384	164
Deferred income taxes, liabilities, gross	3,585	1,992
Deferred income taxes, liabilities	$ 3,585	$ 1,992