Collateral (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Cash equivalents(1)	$ 1,324	$ 1,295
Pledged securities at market value	154	170
Letters of credit	1,477	1,311
Guarantees	1,369	1,418
Total	$ 4,324	$ 4,194