Investment Securities (Narrative) (Details)	3 Months Ended
Mar. 31, 2012
Investment Securities [Abstract]
Underlying mortgages of held-to-maturity securities with other-than-temporary impairment, loan-to-value	69.00%
Underlying borrowers, FICO score, weighted average	731
Portion of underlying mortgages with limited documentation	59.00%

This item represents the loan to collateral ratio of the underlying assets in the security, represented as a percentage, which was considered as one of the potential factors in reaching a conclusion that the held-to-maturity investments are other than temporarily impaired and only the amount of impairment related to credit loss was recognized in earnings.

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 18A

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration