Loans and asset quality- Details of Loan Distribution and Industry Concentrations of Credit Risk (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Jun. 30, 2014	Dec. 31, 2013		Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 57,527	[1]		$ 51,657	[1]
Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	14,574			14,359
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,558			1,647
Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	10,825			9,818
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,403			2,010
Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,262			1,385
Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,301			3,715
Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,548			15,652
Domestic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	42,098			38,230
Domestic | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,465			4,511
Domestic | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,317			1,534
Domestic | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	10,733			9,743
Domestic | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,390			2,001
Domestic | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,293			1,322
Domestic | Other residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,262			1,385
Domestic | Overdrafts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,235		1,748	1,314		1,487
Domestic | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	855		842	768		701
Domestic | Margin loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,548		17,685	15,652		15,146
Foreign
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,429			13,427
Foreign | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	9,109			9,848
Foreign | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	241			113
Foreign | Wealth management loans and mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	92			75
Foreign | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	13			9
Foreign | Lease financings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	879			945
Foreign | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 5,095			$ 2,437

[1] Net of unearned income of $894 million at Sept. 30, 2014 and $1,020 million at Dec. 31, 2013 primarily on domestic and foreign lease financings.