Financial Statements - Carrying Amounts and Classification of Assets and Liabilities for Consolidated VIEs (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Sep. 30, 2016
Variable Interest Entity [Line Items]
Current assets	$ 13,229	$ 17,109
Current liabilities	10,742	16,331
Long-term liabilities	18,496	21,524
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Current assets	2	284
Noncurrent assets	53	98
Total assets	55	382
Current liabilities	3	230
Long-term liabilities	44	29
Total liabilities	$ 47	$ 259