Credit Quality Indicators - Commercial Portfolio Credit Risk Profile by Creditworthiness Category (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 43,028	$ 43,979
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,179	1,280
Commercial | Investment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	793	906
Commercial | Noninvestment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	386	374
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,441	1,449
Commercial Real Estate | Investment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	1,005	1,062
Commercial Real Estate | Noninvestment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	436	387
Financial Institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	10,973	11,144
Financial Institutions | Investment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	9,552	9,643
Financial Institutions | Noninvestment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,421	$ 1,501