Income Taxes - Deferred Income Taxes (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Compensation and benefits, assets	$ 618	$ 720
Loss and credit carryforwards, assets	1,098	1,101
Other, assets	531	783
Deferred income taxes, assets, gross	2,247	2,604
Valuation allowance, assets	(1,032)	(997)
Deferred income taxes, assets	1,216	1,606
Property and equipment, liabilities	244	164
Deferred Tax Liabilities, Other Finite-Lived Assets	1,584	1,571
Other, liabilities	164	664
Deferred income taxes, liabilities, gross	1,992	2,399
Deferred income taxes, liabilities	$ 1,992	$ 2,399