Accounting Changes - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax provision	$ 18	$ 38	$ 148	$ 75
Excess Tax Benefit from Share-based Compensation, Operating Activities			(48)	$ 0
New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax provision	$ 21		$ 48
Weighted Average Number of Shares Outstanding, Basic, Increase (Decrease)			1
Excess Tax Benefit from Share-based Compensation, Operating Activities			$ 48