Contingent Liabilities and Guarantees - Guarantees (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	$ 14,729
Liability Recorded	98
Written Put Options [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	2,573
Liability Recorded	20
Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	10,757
Liability Recorded	68
Recourse Agreement with FNMA [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	1,394
Liability Recorded	5
Return Guarantee Agreement with LIHTC Investors [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	5
Liability Recorded	$ 5