Investment Securities (Net Realized Investment Gains (Losses)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Investment securities
Trading Securities, Realized Gain (Loss)	$ 12.6	$ 31.5	$ 77.6	$ 50.0
Trading securities, tax on realized and unrealized holding gain (loss) on investments	(0.4)	(9.4)	(17.8)	(15.3)
Trading securities realized and unrealized holding gain (loss) on investments after tax	12.2	22.1	59.8	34.7
Foreign Currency Transaction Gain (Loss), Realized	(0.9)	(7.8)	(17.4)	(9.5)
Trading securities, unrealized foreign currency transaction gain (loss) tax	0.4	2.0	5.1	2.5
Trading securities, unrealized foreign currency gain (loss) net of tax	(0.5)	(5.8)	(12.3)	(7.0)
Trading Securities, Realized Gain (Loss), Total	11.7	23.7	60.2	40.5
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	0	(7.4)	(12.7)	(12.8)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	11.7	16.3	47.5	27.7
Fixed maturity investments.
Investment securities
Trading Securities, Realized Gain (Loss)	(9.1)	32.2	12.9	73.5
Foreign Currency Transaction Gain (Loss), Realized	(0.3)	(3.2)	(14.4)	(4.0)
Trading Securities, Realized Gain (Loss), Total	(9.4)	29.0	(1.5)	69.5
Short-term investments
Investment securities
Trading Securities, Realized Gain (Loss)	0	0	0.2	0
Foreign Currency Transaction Gain (Loss), Realized	(0.6)	(3.4)	0	(3.9)
Trading Securities, Realized Gain (Loss), Total	(0.6)	(3.4)	0.2	(3.9)
Common equity securities
Investment securities
Trading Securities, Realized Gain (Loss)	23.5	3.9	60.7	(2.2)
Foreign Currency Transaction Gain (Loss), Realized	(3.0)	0	(3.0)	0
Trading Securities, Realized Gain (Loss), Total	20.5	3.9	57.7	(2.2)
Convertible fixed maturity investments
Investment securities
Trading Securities, Realized Gain (Loss)	(0.2)	1.1	(0.7)	3.2
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Trading Securities, Realized Gain (Loss), Total	(0.2)	1.1	(0.7)	3.2
Other long-term investments
Investment securities
Trading Securities, Realized Gain (Loss)	(1.1)	(6.0)	4.8	(24.8)
Foreign Currency Transaction Gain (Loss), Realized	3.0	(1.2)	0	(1.6)
Trading Securities, Realized Gain (Loss), Total	1.9	(7.2)	4.8	(26.4)
Forward Contracts
Investment securities
Trading Securities, Realized Gain (Loss)	(0.5)	0.3	(0.3)	0.3
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Trading Securities, Realized Gain (Loss), Total	$ (0.5)	$ 0.3	$ (0.3)	$ 0.3

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

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-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

-Paragraph 9

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