Contingent Liabilities and Guarantees - Guarantees (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	$ 14,146
Liability Recorded	129
Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	10,711
Liability Recorded	79
Recourse Agreement with FNMA [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	1,254
Liability Recorded	5
Return Guarantee Agreement with LIHTC Investors [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	16
Liability Recorded	16
Written Put Options [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	2,165
Liability Recorded	$ 29