Credit Quality Indicators - Commercial Portfolio - Credit Risk Profile by Creditworthiness Category (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 45,431	$ 43,979
Commercial
Financing Receivable, Recorded Investment [Line Items]
Loans	1,387	1,280
Commercial | Investment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	1,018	906
Commercial | Noninvestment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	369	374
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Loans	1,595	1,449
Commercial Real Estate | Investment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	1,113	1,062
Commercial Real Estate | Noninvestment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	482	387
Financial Institutions
Financing Receivable, Recorded Investment [Line Items]
Loans	10,516	11,144
Financial Institutions | Investment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	8,899	9,643
Financial Institutions | Noninvestment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 1,617	$ 1,501