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Investment Securities (Non-agency Residential 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 |
Residential | Prime [Member] |  |  |
Investment securities |  |  |
Fair value investments | 133.1 |  |
Residential | Non-prime |  |  |
Investment securities |  |  |
Fair value investments | 0.1 |  |
Residential | Subprime [Member] |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Residential | Super Senior |  |  |
Investment securities |  |  |
Fair value investments | 65.6 |  |
Residential | Super Senior | Prime [Member] |  |  |
Investment securities |  |  |
Fair value investments | 65.6 |  |
Residential | Super Senior | Non-prime |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Residential | Super Senior | Subprime [Member] |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Residential | Senior |  |  |
Investment securities |  |  |
Fair value investments | 67.6 |  |
Residential | Senior | Prime [Member] |  |  |
Investment securities |  |  |
Fair value investments | 67.5 |  |
Residential | Senior | Non-prime |  |  |
Investment securities |  |  |
Fair value investments | 0.1 |  |
Residential | Senior | Subprime [Member] |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Residential | Subordinate |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Residential | Subordinate | Prime [Member] |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Residential | Subordinate | Non-prime |  |  |
Investment securities |  |  |
Fair value investments | 0.0 |  |
Residential | Subordinate | Subprime [Member] |  |  |
Investment securities |  |  |
Fair value investments | $ 0.0 |  |

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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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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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