Loans and asset quality- Credit Quality Indicators - Wealth Management Loans and Mortgages - Credit Risk Profile by Internally Assigned Grade (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 49,224	$ 46,629
Wealth Management Loans Portfolio Segment \| Investment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	4,583	4,597
Wealth Management Loans Portfolio Segment \| Noninvestment grade
Financing Receivable, Recorded Investment [Line Items]
Loans	121	125
Wealth Management Mortgages Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Loans	4,287	4,142
Wealth management loans and mortgages
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 8,991	$ 8,864

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.3)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Article 5

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant