Loans and Allowance for Losses and Concentrations of Credit Risk - Troubled Debt Restructurings (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 defaulted_loan	Sep. 30, 2013 defaulted_loan
Receivables [Abstract]
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 4.5	$ 0.2	$ 5.3	$ 1.1
Financing Receivable, Modifications, Post-Modification Recorded Investment	5.1	0.2	6.0	1.1
Financing Receivable, Modifications, Subsequent Default, Number of Contracts			0	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment			$ 0	$ 0.2

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953676-111524

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- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 34

-URI http://asc.fasb.org/extlink&oid=28368275&loc=SL6953682-111524

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- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

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