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Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2016 | Jun. 30, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | $ 25.6 | $ (59.1) | $ (204.5) | $ (43.9)
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments | (9.5) | 17.3 | 24.9 | 14.7
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax | 16.1 | (41.8) | (179.6) | (29.2)
Foreign Currency Transaction Gain (Loss), Unrealized | (0.2) | 1.8 | 2.6 | (3.2)
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax | 0.0 | (0.1) | 0.0 | (0.1)
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax | (0.2) | 1.7 | 2.6 | (3.3)
Net unrealized investment gains (losses), pre-tax | 25.4 | (57.3) | (201.9) | (47.1)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax | (9.5) | 17.2 | 24.9 | 14.6
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax | 15.9 | (40.1) | (177.0) | (32.5)
Fixed maturity investments. |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | 20.7 | (13.4) | 42.4 | (2.0)
Foreign Currency Transaction Gain (Loss), Unrealized | 0.0 | 0.0 | 0.0 | 0.0
Net unrealized investment gains (losses), pre-tax | 20.7 | (13.4) | 42.4 | (2.0)
Short-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | 0.0 | 0.0 | 0.0 | 0.0
Foreign Currency Transaction Gain (Loss), Unrealized | 0.0 | 0.0 | 0.0 | 0.0
Net unrealized investment gains (losses), pre-tax | 0.0 | 0.0 | 0.0 | 0.0
Common equity securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | (10.6) | (22.6) | (260.4) | (25.3)
Foreign Currency Transaction Gain (Loss), Unrealized | 0.0 | 1.6 | 2.4 | (2.4)
Net unrealized investment gains (losses), pre-tax | (10.6) | (21.0) | (258.0) | (27.7)
Other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Unrealized gains (losses) on investments | 15.5 | (23.1) | 13.5 | (16.6)
Foreign Currency Transaction Gain (Loss), Unrealized | (0.2) | 0.2 | 0.2 | (0.8)
Net unrealized investment gains (losses), pre-tax | $ 15.3 | $ (22.9) | $ 13.7 | $ (17.4)

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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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