Loans and asset quality- Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended				3 Months Ended				3 Months Ended					9 Months Ended
	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2014 Other residential mortgages Contract	Dec. 31, 2013 Other residential mortgages	Sep. 30, 2014 Wealth management mortgages	Dec. 31, 2013 Wealth management mortgages	Sep. 30, 2014 Wealth management mortgages California State	Sep. 30, 2014 Wealth management mortgages New York State	Sep. 30, 2014 Wealth management mortgages Massachusetts	Sep. 30, 2014 Wealth management mortgages Florida	Sep. 30, 2014 Wealth management mortgages Other	Sep. 30, 2014 Overdrafts	Dec. 31, 2013 Overdrafts	Sep. 30, 2014 Margin loans	Dec. 31, 2013 Margin loans	Sep. 30, 2014 Domestic	Dec. 31, 2013 Domestic	Sep. 30, 2014 Domestic Other residential mortgages	Dec. 31, 2013 Domestic Other residential mortgages	Sep. 30, 2014 Domestic Overdrafts	Jun. 30, 2014 Domestic Overdrafts	Dec. 31, 2013 Domestic Overdrafts	Sep. 30, 2013 Domestic Overdrafts	Sep. 30, 2014 Domestic Margin loans	Jun. 30, 2014 Domestic Margin loans	Dec. 31, 2013 Domestic Margin loans	Sep. 30, 2013 Domestic Margin loans	Sep. 30, 2014 Domestic Margin loans Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Subsequently defaulted number of contracts (contracts)					10
Subsequently defaulted recorded investment					$ 2
Loan to value ratio at origination (percent)							65.00%
Percentage of past due mortgages (percent)							1.00%
Geographic concentrations (percent)									21.00%	21.00%	15.00%	9.00%	34.00%
Loans	57,527	[1]	51,657	[1]	1,262	1,385	5,359	4,834						6,301	3,715	17,548	15,652	42,098	38,230	1,262	1,385	1,235	1,748	1,314	1,487	17,548	17,685	15,652	15,146
Purchased mortgages																				$ 366
Purchased residential mortgages, loan to value ratio (percent)																				76.00%
Percentage of purchased residential mortgages that were at least 60 days delinquent (percent)																				18.00%
Number of business days in which overdrafts are generally repaid	2 days													2 days
Required daily collateral margin (percent)																														100.00%

[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.