Collateral (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Sep. 30, 2016
Business Acquisition [Line Items]
Cash equivalents(1)	$ 1,283	$ 1,295
Pledged securities at market value	166	170
Letters of credit	1,328	1,311
Guarantees	1,443	1,418
Total	$ 4,220	$ 4,194