Loans and asset quality- Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended						3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Other residential mortgages Contract	Dec. 31, 2012 Other residential mortgages	Mar. 31, 2013 Wealth Management Mortgages Portfolio Segment	Dec. 31, 2012 Wealth Management Mortgages Portfolio Segment	Mar. 31, 2013 Wealth Management Mortgages Portfolio Segment New York State	Mar. 31, 2013 Wealth Management Mortgages Portfolio Segment California State	Mar. 31, 2013 Wealth Management Mortgages Portfolio Segment Massachusetts	Mar. 31, 2013 Wealth Management Mortgages Portfolio Segment Florida	Mar. 31, 2013 Wealth Management Mortgages Portfolio Segment Other	Mar. 31, 2013 Overdrafts	Dec. 31, 2012 Overdrafts	Mar. 31, 2013 Margin loans	Dec. 31, 2012 Margin loans	Mar. 31, 2013 Domestic	Dec. 31, 2012 Domestic	Mar. 31, 2013 Domestic Other residential mortgages	Dec. 31, 2012 Domestic Other residential mortgages	Mar. 31, 2013 Domestic Overdrafts	Dec. 31, 2012 Domestic Overdrafts	Mar. 31, 2012 Domestic Overdrafts	Mar. 31, 2013 Domestic Margin loans	Dec. 31, 2012 Domestic Margin loans	Mar. 31, 2012 Domestic Margin loans	Mar. 31, 2013 Domestic Margin loans Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Subsequently defaulted number of contracts (contracts)			15
Subsequently defaulted recorded investment			$ 4
Loan to value ratio at origination (percent)					63.00%
Percentage of past due mortgages (percent)					1.00%
Geographic concentrations (percent)							22.00%	20.00%	16.00%	8.00%	34.00%
Loans	49,224	46,629	1,570	1,632	4,287	4,142						5,319	5,298	13,242	13,397	36,535	36,459	1,570	1,632	2,772	2,228	1,971	13,242	13,397	13,144
Purchased mortgages																		$ 480
Purchased residential mortgages, loan to value ratio (percent)																		75.00%
Percentage of purchased residential mortgages that were at least 60 days delinquent (percent)																		23.00%
Number of business days in which overdrafts are generally repaid	2 days											2 days
Required daily collateral margin (percent)																										100.00%