Loans - Impaired Commercial Loans Considered as TDR Loans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Impaired commercial loans as TDR	$ 1,391	$ 1,102
Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Impaired commercial loans as TDR	492	473
Unpaid principal balance of impaired commercial loans	945	1,194
Commercial Loans [Member] | Construction and Other Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired commercial loans as TDR	375	342
Unpaid principal balance of impaired commercial loans	565	784
Commercial Loans [Member] | Business Banking and Middle Markets Enterprises [Member]
Financing Receivable, Impaired [Line Items]
Impaired commercial loans as TDR	84	94
Unpaid principal balance of impaired commercial loans	148	180
Commercial Loans [Member] | Other Commercial [Member]
Financing Receivable, Impaired [Line Items]
Impaired commercial loans as TDR	33	37
Unpaid principal balance of impaired commercial loans	89	93
Commercial Loans [Member] | Global Banking [Member]
Financing Receivable, Impaired [Line Items]
Unpaid principal balance of impaired commercial loans	$ 143	$ 137