Financial Statements - Carrying Amounts and Classification of Assets and Liabilities for Consolidated VIEs (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015
Variable Interest Entity [Line Items]
Current assets	$ 11,058	$ 10,469	$ 11,721
Current liabilities	11,792	10,446	11,909
Noncurrent liabilities	8,288	8,398	8,067
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Current assets	308	281	269
Noncurrent assets	123	128	134
Total assets	431	409	403
Current liabilities	225	232	200
Noncurrent liabilities	32	34	35
Total liabilities	$ 257	$ 266	$ 235