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Investment Securities (Net Realized Investment Gains (Losses)) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2015 | Sep. 30, 2014 | Sep. 30, 2015 | Sep. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | $ (7.4) | $ 58.0 | $ 49.3 | $ 97.1
Trading securities, Tax on Realized Holding Gain (Loss) on Investments | 1.5 | (7.0) | (15.7) | (13.3)
Trading securities realized holding gain (loss) on investments after tax | (5.9) | 51.0 | 33.6 | 83.8
Foreign Currency Transaction Gain (Loss), Realized | 0.0 | (0.1) | 0.4 | (0.1)
Trading Securities, Tax on Realized Foreign Currency Transaction Gain (Loss) Tax | 0.0 | 0.0 | 0.0 | 0.0
Trading securities, realized foreign currency gain (loss) net of tax | 0.0 | (0.1) | 0.4 | (0.1)
Trading Securities, Realized Gain (Loss), Total | (7.4) | 57.9 | 49.7 | 97.0
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | 1.5 | (7.0) | (15.7) | (13.3)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax | (5.9) | 50.9 | 34.0 | 83.7
Fixed maturity investments. |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | (0.1) | 2.3 | 2.0 | 4.7
Foreign Currency Transaction Gain (Loss), Realized | 0.0 | (0.1) | 0.0 | (0.1)
Trading Securities, Realized Gain (Loss), Total | (0.1) | 2.2 | 2.0 | 4.6
Short-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | 0.0 | 0.0 | 0.0 | 0.0
Foreign Currency Transaction Gain (Loss), Realized | 0.0 | 0.0 | 0.0 | 0.0
Trading Securities, Realized Gain (Loss), Total | 0.0 | 0.0 | 0.0 | 0.0
Common equity securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | (5.9) | 51.4 | 41.6 | 83.2
Foreign Currency Transaction Gain (Loss), Realized | 0.0 | 0.0 | 0.4 | 0.0
Trading Securities, Realized Gain (Loss), Total | (5.9) | 51.4 | 42.0 | 83.2
Convertible fixed maturity investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | 0.0 | 1.6 | (4.3) | 6.5
Foreign Currency Transaction Gain (Loss), Realized | 0.0 | 0.0 | 0.0 | 0.0
Trading Securities, Realized Gain (Loss), Total | 0.0 | 1.6 | (4.3) | 6.5
Other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | (1.4) | 2.7 | 10.0 | 2.7
Foreign Currency Transaction Gain (Loss), Realized | 0.0 | 0.0 | 0.0 | 0.0
Trading Securities, Realized Gain (Loss), Total | $ (1.4) | $ 2.7 | $ 10.0 | $ 2.7

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