Significant Accounting Policies (Nonmarketable Equity Securities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Corporation's ownership in FHLB stock	$ 17.2	$ 17.2
Corporation's ownership in FRB stock	$ 8.4	$ 8.4

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 325

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6478792&loc=d3e63345-112809

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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Paragraph 26

-IssueDate 2006-05-01

-Chapter 12

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

Name:	us-gaap_FederalHomeLoanBankStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant