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Investment Securities (Net Realized and Unrealized Investement Gains and Losses) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investment securities
Net foreign currency gains (losses)	$ (57.2)	$ 20.7	$ (76.0)
Total net realized and unrealized gains (losses) reflected in earnings	118.2	74.1	77.6
Net Realized and Unrealized Gain (Loss) on Trading Securities	175.4	53.4	153.6
Trading securities, unrealized gain (loss), net of tax	(41.7)	(13.0)	(41.6)
Trading securities, unrealized foreign currency gain (loss) net of tax	14.9	(5.1)	20.1
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	(26.8)	(18.1)	(21.5)
Trading securities, unrealized gain (loss), net of tax	133.7	40.4	112.0
Trading securities, unrealized foreign currency gain (loss) net of tax	(42.3)	15.6	(55.9)
Net unrealized gain (loss) and foreign currency gain (loss) on trading securities net of tax	91.4	56.0	56.1
Trading securities realized gain	162.2	191.6	205.0
Trading securities realized loss	94.1	123.3	73.6
Accounts payable on unsettled investment purchases	11.4	34.6
Accounts receivable on unsettled investment sales	3.9	4.7
Fixed maturity investments
Investment securities
Net foreign currency gains (losses)	(48.4)	30.6	(61.6)
Total net realized and unrealized gains (losses) reflected in earnings	52.6	87.6	(32.1)
Net Realized and Unrealized Gain (Loss) on Trading Securities	101.0	57.0	29.5
Short-term investments
Investment securities
Net foreign currency gains (losses)	(4.2)	(11.0)	(9.1)
Total net realized and unrealized gains (losses) reflected in earnings	(4.2)	(11.0)	(9.1)
Net Realized and Unrealized Gain (Loss) on Trading Securities	0	0	0
Common equity securities
Investment securities
Net foreign currency gains (losses)	(0.1)	(1.8)	(8.0)
Total net realized and unrealized gains (losses) reflected in earnings	67.1	(7.8)	71.3
Net Realized and Unrealized Gain (Loss) on Trading Securities	67.2	(6.0)	79.3
Convertible fixed maturity investments
Investment securities
Net foreign currency gains (losses)	0	0	0
Total net realized and unrealized gains (losses) reflected in earnings	2.5	(13.7)	11.3
Net Realized and Unrealized Gain (Loss) on Trading Securities	2.5	(13.7)	11.3
Other long-term investments
Investment securities
Net foreign currency gains (losses)	(4.5)	2.9	2.7
Total net realized and unrealized gains (losses) reflected in earnings	0.5	19.0	36.2
Trading Securities, Change in Unrealized Holding Gain (Loss)		16.1	33.5
Net Realized and Unrealized Gain (Loss) on Trading Securities	5.0
Forward contracts
Investment securities
Net foreign currency gains (losses)	0
Total net realized and unrealized gains (losses) reflected in earnings	(0.3)
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ (0.3)

X

- Definition

The sum of the realized and unrealized net gain (loss) on trading securities during the period.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



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Aggregate amounts payable to broker-dealers and clearing organizations include amounts payable for securities failed to receive, certain deposits received for securities loaned, amounts payable to clearing organizations on open transactions, and floor-brokerage payables. In addition, the net receivable or payable arising from unsettled trades would be reflected in those captions. A broker-dealer that purchases securities, either for its own account or for a customer's account, but does not receive the securities on the settlement date records the amount of money representing the purchase price of the securities, including any accrued interest, as a liability to the selling broker-dealer. This liability is paid when the securities are received by the purchasing broker-dealer.

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Amount receivable from securities failed to deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage items. Also cash and securities [guarantee] on deposit with [commodities] clearing organizations and other entities which provide services necessary to operations of the Company. This item would include, for instance, cash and securities advanced as [refundable] collateral for securities borrowed.

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This item represents the gain realized during the period from the sale of trading securities.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of trading securities held at each balance sheet date, that was included in earnings for the period. Trading securities are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) and the change in net unrealized holding gain (loss) is included in earnings for the period.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



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The 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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Net Realized and Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax

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Represents the net realized and unrealized investment gains (losses) after income taxes.

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Represents the income taxes attributable to realized and unrealized gains (losses) on trading securities.

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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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The unrealized foreign currency transaction gain (loss) as of the balance sheet date which is included in net income before tax during the reporting period.

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The tax expense (benefit) 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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