Loans and asset quality- Allowance for Credit Losses Activity (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	$ 50,138		$ 46,629
Domestic
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	36,665		36,459
Overdrafts
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	4,837		5,298
Overdrafts | Domestic
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	1,487	1,762	2,228	2,070
Margin loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	15,146		13,397
Margin loans | Domestic
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	15,146	14,434	13,397	13,036
Other | Domestic
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans	$ 701	$ 657	$ 639	$ 685