Significant Accounting Policies (Nonmarketable Equity Securities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Corporation's ownership in FHLB stock	$ 19.0us-gaap_FederalHomeLoanBankStock	$ 17.2us-gaap_FederalHomeLoanBankStock
Corporation's ownership in FRB stock	$ 8.4us-gaap_FederalReserveBankStock	$ 8.4us-gaap_FederalReserveBankStock

Federal Reserve Bank stock represents an equity interest in the Federal Reserve Bank. 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

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