Loans - Components of Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total commercial	$ 42,568	$ 33,649
Total consumer	18,884	18,218
Total	61,452	51,867	49,600
Construction and Other Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total commercial	7,920	7,860
Business Banking and Middle Markets Enterprises [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total commercial	12,497	10,225
Global Banking [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total commercial	19,011	12,658
Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total commercial	3,140	2,906
Home Equity Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	2,387	2,563
Other Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	15,086	14,113
Credit Card Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	796	828
Other Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total consumer	$ 615	$ 714