Investment Securities (Net Realized Investment Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	$ 25.9	$ 25.3
Trading securities, tax on realized holding gain (loss) on investments	(6.5)	(4.6)
Trading securities realized holding gain (loss) on investments after tax	19.4	20.7
Foreign Currency Transaction Gain (Loss), Realized	26.9	(3.6)
Trading securities, realized foreign currency transaction gain (loss) t	(6.7)	0.9
Trading securities, realized foreign currency gain (loss) net of tax	20.2	(2.7)
Trading Securities, Realized Gain (Loss), Total	52.8	21.7
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(13.2)	(3.7)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	39.6	18.0
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	9.8	4.4
Foreign Currency Transaction Gain (Loss), Realized	21.2	(3.5)
Trading Securities, Realized Gain (Loss), Total	31.0	0.9
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0	0
Foreign Currency Transaction Gain (Loss), Realized	3.5	0
Trading Securities, Realized Gain (Loss), Total	3.5	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	24.4	18.9
Foreign Currency Transaction Gain (Loss), Realized	1.1	(0.1)
Trading Securities, Realized Gain (Loss), Total	25.5	18.8
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(4.2)	2.4
Foreign Currency Transaction Gain (Loss), Realized	0	0
Trading Securities, Realized Gain (Loss), Total	(4.2)	2.4
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(4.1)	(0.3)
Foreign Currency Transaction Gain (Loss), Realized	1.1	0
Trading Securities, Realized Gain (Loss), Total	(3.0)	(0.3)
Forward Contracts
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0	(0.1)
Foreign Currency Transaction Gain (Loss), Realized	0	0
Trading Securities, Realized Gain (Loss), Total	$ 0	$ (0.1)

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30690-110894

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 830

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+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 7

-Subparagraph c

-Article 5

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

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

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