Loans and leases and the allowance for credit losses (Details) (Textual) (USD $) In Millions	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Loans and leases and allowance for credit losses (Details) (Textual) [Abstract]
Interest income on loans acquired	$ 97	$ 46	$ 207	$ 132
Contractual principal and interest payments	704		704		97
Purchased impaired loans as a percentage of total assets			Less than 1% of companys assets		Less than .2% of companys assets
Interest income earned on purchased impaired loans	$ 11	$ 2	$ 18	$ 4
Loan delinquent period	90 days or more
Delinquency period for loan-by-loan evaluation of collectability on residential real estate loans and home equity loans and lines of credit	more than 150 days

The price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 03-3

-Paragraph 16

-Subparagraph a(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 15

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6891207&loc=d3e13503-111538

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

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Period Type:	instant