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Investment Securities (Non-agency Mortgage-backed Securities) (Details) - USD ($) $ in Millions | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
--- | --- | --- | ---
Investment securities |  |  |
Fair value investments | $ 4,050.9 | $ 3,343.6 | $ 3,889.0
Residential |  |  |
Investment securities |  |  |
Fair value investments | 133.2 | 71.0 |
Commercial |  |  |
Investment securities |  |  |
Fair value investments | 140.4 | 109.3 |
Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 273.6 | $ 180.3 |
Securities Issued in 2004 [Member] | Residential |  |  |
Investment securities |  |  |
Fair value investments | 17.3 |  |
Securities Issued in 2004 [Member] | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Securities Issued in 2004 [Member] | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 17.3 |  |
2005 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 8.6 |  |
2005 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2005 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 8.6 |  |
2006 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 3.9 |  |
2006 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2006 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 3.9 |  |
2007 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2007 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2007 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2008 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 3.6 |  |
2008 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2008 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 3.6 |  |
2009 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2009 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2009 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2010 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 15.2 |  |
2010 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 5.4 |  |
2010 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 20.6 |  |
2011 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 13.5 |  |
2011 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
2011 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 13.5 |  |
2012 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 9.8 |  |
2012 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 18.0 |  |
2012 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 27.8 |  |
2013 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 14.0 |  |
2013 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 17.2 |  |
2013 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 31.2 |  |
2014 | Residential |  |  |
Investment securities |  |  |
Fair value investments | 47.3 |  |
2014 | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 55.0 |  |
2014 | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | 102.3 |  |
Securities Issued in 2015 [Member] | Residential |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Securities Issued in 2015 [Member] | Commercial |  |  |
Investment securities |  |  |
Fair value investments | 44.8 |  |
Securities Issued in 2015 [Member] | Total Non-agency |  |  |
Investment securities |  |  |
Fair value investments | $ 44.8 |  |

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- Definition Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph a, f, g -Article 7 + Details
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