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Investment Securities (Debt Securities Issued By Corporation) (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
Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 1,000.0 | 1,171.7 |
Other Standard Poors Rating [Member] | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 0.0 | 5.4 |
BBB | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 507.1 | 426.5 |
A | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | 397.7 | 594.9 |
AA | Debt securities issued by corporations |  |  |
Investment securities |  |  |
Fair value investments | $ 95.2 | $ 144.9 |

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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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