Property, Equipment and Technology, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Technology, accumulated amortization	$ 2,300	$ 1,900
Depreciation and amortization	656	613	$ 556
Depreciation and amortization, amortization expense on technology	60	55	56
Property, Equipment and Technology
Finite-Lived Intangible Assets [Line Items]
Depreciation and amortization	596	558	500
Technology and Software
Finite-Lived Intangible Assets [Line Items]
Depreciation and amortization, amortization expense on technology	$ 357	$ 312	$ 285