Investment Securities Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	$ (66.2)	$ 38.9	$ 98.7
Foreign Currency Transaction Gain (Loss), Unrealized	116.3	18.3	(48.6)
Net unrealized investment gains, pre-tax	50.1	57.2	50.1
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments	6.0	8.2	(17.9)
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax	(28.0)	(5.6)	12.7
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	(22.0)	2.6	(5.2)
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax	(60.2)	47.1	80.8
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax	88.3	12.7	(35.9)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	28.1	59.8	44.9
Fixed maturity investments
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	30.9	(93.9)	18.5
Foreign Currency Transaction Gain (Loss), Unrealized	111.7	15.3	(45.9)
Net unrealized investment gains, pre-tax	142.6	(78.6)	(27.4)
Short-term investments
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	(0.2)	0.1	0
Foreign Currency Transaction Gain (Loss), Unrealized	0.1	0	0.1
Net unrealized investment gains, pre-tax	(0.1)	0.1	0.1
Common equity securities
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	(83.0)	119.2	65.9
Foreign Currency Transaction Gain (Loss), Unrealized	(0.1)	(0.4)	(0.1)
Net unrealized investment gains, pre-tax	(83.1)	118.8	65.8
Convertible fixed maturity and preferred investments
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	(8.2)	3.2	1.1
Foreign Currency Transaction Gain (Loss), Unrealized	0.4	0	0
Net unrealized investment gains, pre-tax	(7.8)	3.2	1.1
Other long-term investments
Investment securities
Trading Securities, Change in Unrealized Holding Gain (Loss)	(5.7)	10.3	13.2
Foreign Currency Transaction Gain (Loss), Unrealized	4.2	3.4	(2.7)
Net unrealized investment gains, pre-tax	$ (1.5)	$ 13.7	$ 10.5

Amount before tax of foreign currency transaction unrealized gain (loss) recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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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.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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The after-tax aggregate of the change in unrealized holding gain (loss) and foreign currency gain (loss) included in earnings during the reporting period.

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The after-tax gain (loss) attributable to the foreign currency transaction gain (loss) on trading securities held at each balance sheet date, that was included in earnings in the period.

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