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Investment Securities Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Investment securities |  |  |
Trading Securities, Change in Unrealized Holding Gain (Loss) | $ 152.9 | $ (79.3) | $ 40.3
Foreign Currency Transaction Gain (Loss), Unrealized | (4.8) | (9.0) | (1.9)
Net unrealized investment gains (losses), pre-tax | 148.1 | (88.3) | 38.4
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments | (12.3) | 9.9 | 3.3
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax | (0.1) | 0.5 | 0.0
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax | (12.4) | 10.4 | 3.3
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax | 140.6 | (69.4) | 43.6
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax | (4.9) | (8.5) | (1.9)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax | 135.7 | (77.9) | 41.7
Fixed maturity investments |  |  |
Investment securities |  |  |
Trading Securities, Change in Unrealized Holding Gain (Loss) | (15.6) | 11.3 | (49.9)
Foreign Currency Transaction Gain (Loss), Unrealized | 0.0 | 0.0 | 0.0
Net unrealized investment gains (losses), pre-tax | (15.6) | 11.3 | (49.9)
Common equity securities |  |  |
Investment securities |  |  |
Trading Securities, Change in Unrealized Holding Gain (Loss) | 207.6 | (83.0) | 86.1
Foreign Currency Transaction Gain (Loss), Unrealized | (3.7) | (7.7) | (1.9)
Net unrealized investment gains (losses), pre-tax | 203.9 | (90.7) | 84.2
Other long-term investments |  |  |
Investment securities |  |  |
Trading Securities, Change in Unrealized Holding Gain (Loss) | (39.1) | (7.6) | 4.1
Foreign Currency Transaction Gain (Loss), Unrealized | (1.1) | (1.3) | 0.0
Net unrealized investment gains (losses), pre-tax | $ (40.2) | $ (8.9) | $ 4.1

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- Definition Amount of unrealized holding gain (loss) recognized in the income statement for investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading. + 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 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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