Commitments, Contingencies, Guarantees, and Others - Guarantees, LOC and Loss Sharing, U.K Cross Sell (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Insurance Claims [Member]
Loss Contingencies [Line Items]
Loss contingency accrual	$ 176	$ 116
Loss accrual increase (decrease)	147
Loss Contingency, Range of Possible Loss, Portion Not Accrued	250
Letter of Credit
Loss Contingencies [Line Items]
Contractual amounts of standby letters of credit and commercial letters of credit	1,900	2,100
Other Liabilities | Letter of Credit
Loss Contingencies [Line Items]
Letters of credit outstanding	3	3
Loss Sharing Agreement
Loss Contingencies [Line Items]
Guarantee obligation	$ 40	$ 36