Income Taxes - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 415	$ 478	$ 620
Unrecognized tax benefits interest and penalties reflected in current year	57	(38)	5
Undistributed earnings of foreign subsidiaries	9,600
Tax reductions related to tax holidays	$ 144	$ 121	$ 103
Income Tax Holiday, Income Tax Benefits Per Share	$ 0.64	$ 0.56	$ 0.48
Income taxes paid, net	$ 265	$ 218	$ 240
Deferred Income Taxes and Other
Income Tax [Line Items]
Indemnification liability, non-current	$ 134