Commitments, Contingencies, Guarantees, and Others - Guarantees, Loss Sharing, U.K Cross Sell (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 5,325	$ 4,782
Insurance Claims [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	300
Loss contingency accrual	238	176
Loss accrual increase (decrease)	161
Loss Sharing Agreement
Loss Contingencies [Line Items]
Guarantee obligation	48	$ 40
Gpm Mfh [Member]
Loss Contingencies [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 420