Commitments and Contingent Liabilities- Summary of Off-Balance Sheet Credit Risks, Net of Participations (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Potential exposure of off-balance sheet credit risks	$ 175
Lending commitments
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Potential exposure of off-balance sheet credit risks	31,522	31,265
Standby letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Potential exposure of off-balance sheet credit risks	7,129	7,167
Commercial letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commercial Letters of Credit	156	219
Securities lending indemnifications
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Potential exposure of off-balance sheet credit risks	$ 251,977	$ 245,717