Loans and asset quality- Details of Loan Distribution and Industry Concentrations of Credit Risk (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 49,224		$ 46,629
Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	13,784		11,288
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,480		1,417
Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,991		8,864
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,874		1,740
Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,570		1,632
Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,319		5,298
Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	13,242		13,397
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	36,535		36,459
Domestic | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,920		5,455
Domestic | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,351		1,306
Domestic | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,919		8,796
Domestic | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,822		1,677
Domestic | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,295	[1]	1,329	[1]
Domestic | Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,570		1,632
Domestic | Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,772		2,228		1,971
Domestic | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	644		639		849
Domestic | Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	13,242		13,397		13,144
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,689		10,170
Foreign | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	8,864		5,833
Foreign | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	129		111
Foreign | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	72		68
Foreign | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	52		63
Foreign | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,025	[1]	1,025	[1]
Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 2,547		$ 3,070

[1] Net of unearned income on domestic and foreign lease financings of $1,106 million at March 31, 2013 and $1,135 million at Dec. 31, 2012.