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Investment Securities (Net Realized Investment Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | $ 27.2 | $ 29.1 | $ 52.5 | $ 80.3
Trading securities, tax on realized holding gain (loss) on investments | (5.3) | (5.5) | (9.9) | (17.3)
Trading securities realized holding gain (loss) on investments after tax | 21.9 | 23.6 | 42.6 | 63.0
Foreign Currency Transaction Gain (Loss), Realized | 3.3 | (6.3) | (0.3) | (20.9)
Trading securities, realized foreign currency transaction gain (loss) t | (1.0) | 1.4 | (0.1) | 4.7
Trading securities, realized foreign currency gain (loss) net of tax | 2.3 | (4.9) | (0.4) | (16.2)
Trading Securities, Realized Gain (Loss), Total | 30.5 | 22.8 | 52.2 | 59.4
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities | (6.3) | (4.1) | (10.0) | (12.6)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax | 24.2 | 18.7 | 42.2 | 46.8
Fixed maturity investments. |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | 5.7 | 6.8 | 10.1 | 29.4
Foreign Currency Transaction Gain (Loss), Realized | 3.0 | (4.0) | (0.5) | (18.6)
Trading Securities, Realized Gain (Loss), Total | 8.7 | 2.8 | 9.6 | 10.8
Short-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | 0 | 0.2 | 0 | 0.1
Foreign Currency Transaction Gain (Loss), Realized | 0 | 0.5 | 0 | 0.7
Trading Securities, Realized Gain (Loss), Total | 0 | 0.7 | 0 | 0.8
Common equity securities |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | 19.4 | 22.7 | 38.3 | 45.3
Foreign Currency Transaction Gain (Loss), Realized | 0 | 0.2 | (0.1) | 0
Trading Securities, Realized Gain (Loss), Total | 19.4 | 22.9 | 38.2 | 45.3
Convertible fixed maturity investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | 1.5 | (3.4) | 3.9 | (0.6)
Foreign Currency Transaction Gain (Loss), Realized | 0 | 0 | 0 | 0
Trading Securities, Realized Gain (Loss), Total | 1.5 | (3.4) | 3.9 | (0.6)
Other long-term investments |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | 0.6 | 3.0 | 0.3 | 5.9
Foreign Currency Transaction Gain (Loss), Realized | 0.3 | (3.0) | 0.3 | (3.0)
Trading Securities, Realized Gain (Loss), Total | 0.9 | 0 | 0.6 | 2.9
Forward Contracts |  |  |  |
Schedule of Trading Securities and Other Trading Assets [Line Items] |  |  |  |
Trading Securities, Realized Gain (Loss) | 0 | (0.2) | (0.1) | 0.2
Foreign Currency Transaction Gain (Loss), Realized | 0 | 0 | 0 | 0
Trading Securities, Realized Gain (Loss), Total | $ 0 | $ (0.2) | $ (0.1) | $ 0.2

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