Loans and asset quality- Allowance for Credit Losses Activity (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	$ 49,224	$ 46,629
Domestic
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	36,535	36,459
Overdrafts
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	5,319	5,298
Overdrafts | Domestic
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	2,772	2,228	1,971
Margin loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	13,242	13,397
Margin loans | Domestic
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	13,242	13,397	13,144
Other | Domestic
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	$ 644	$ 639	$ 849