Loans and asset quality- Details of Loan Distribution and Industry Concentrations of Credit Risk (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 62,326	[1]	$ 59,132	[1]
Unearned income on lease financings	843		866
Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	14,667		13,319
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,971		1,642
Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	11,649		11,184
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,062		2,530
Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,181		1,222
Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,993		5,882
Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	19,566		20,034
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	46,376		45,611
Domestic | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,665		5,603
Domestic | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,686		1,390
Domestic | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	11,547		11,095
Domestic | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,021		2,524
Domestic | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,197		1,282
Domestic | Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,181		1,222
Domestic | Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,513		1,348		1,078
Domestic | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,107		1,113		788
Domestic | Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	19,459		20,034		16,430
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,950		13,521
Foreign | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	9,002		7,716
Foreign | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	285		252
Foreign | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	102		89
Foreign | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	41		6
Foreign | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	893		889
Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,520		4,569
Foreign | Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 107		$ 0

[1] Net of unearned income of $843 million at March 31, 2015 and $866 million at Dec. 31, 2014 primarily on domestic and foreign lease financings.