Income Taxes Deferred Taxes Classified in Consolidated Statements of Financial Position (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Other noncurrent assets	$ 2,360	$ 2,467
Other noncurrent liabilities	(1,733)	(1,542)
Net deferred tax asset	$ 627	$ 925