Investment Securities Available for Sale (Narrative) (Details) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investments [Abstract]
Pledged to secure deposits	$ 2,280,000,000	$ 2,480,000,000
Other-than-temporary impairment charges	$ 500,000	$ 1,600,000	$ 2,200,000

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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