Investment Securities (Details 2) (USD $) In Millions	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Net Realized and Unrealized Investment Gains and Losses
Net realized and unrealized investment (losses) gains	$ 57.3	$ 11.1	$ 76.6	$ 93.1
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	45.1	32.5	72.4	62.3
Income taxes attributable to realized investment gains (losses)	(11.1)	(5.0)	(23.7)	(15.6)
Net realized investment gains (losses), after-tax	34.0	27.5	48.7	46.7
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	(14.0)	(58.6)	(0.2)	1.0
Income taxes attributable to unrealized investment gains (losses)	1.9	(15.3)	2.1	6.4
Net unrealized investment gains (losses), after-tax	(12.1)	(73.9)	1.9	7.4
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	26.2	37.2	4.4	29.8
Income taxes attributable to unrealized investment gains, net foreign exchange gains (losses)	(6.7)	9.7	(1.0)	7.4
Net unrealized investment gains (losses), net foreign exchange gains (losses), after tax	19.5	46.9	3.4	37.2
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	12.2	(21.4)	4.2	30.8
Income taxes attributable to unrealized investment gains (losses), total changes in fair value reflected in earnings	(4.8)	(5.6)	1.1	13.8
Net unrealized investment gains (losses) after-tax, total changes in fair value reflected in earnings	7.4	(27.0)	5.3	44.6
Fixed maturity investments
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	18.1	7.9	19.5	33.4
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	17.2	8.5	9.2	33.1
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	25.5	30.9	10.2	27.6
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	42.7	39.4	19.4	60.7
Short-term investments
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax		(1.6)
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(0.4)	1.1	(1.0)	(0.8)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	(0.4)	(0.5)	(1.0)	(0.8)
Common Equity Securities
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	15.7	17.7	17.9	20.4
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	(18.8)	(46.4)	5.9	(32.5)
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(0.1)	2.3	(0.9)	1.1
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	(18.9)	(44.1)	5.0	(31.4)
Convertible fixed maturity investments
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	2.9	9.5	7.0	13.7
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	(6.0)	(13.9)	(8.1)	(11.1)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	(6.0)	(13.9)	(8.1)	(11.1)
Other long-term investments.
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	8.4	(2.6)	28.0	(5.2)
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	(6.4)	(5.2)	(7.2)	11.5
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	1.2	2.9	(3.9)	1.9
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	$ (5.2)	$ (2.3)	$ (11.1)	$ 13.4

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

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