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Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	$ 25.6	$ (59.1)	$ (204.5)	$ (43.9)
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments	(9.5)	17.3	24.9	14.7
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax	16.1	(41.8)	(179.6)	(29.2)
Foreign Currency Transaction Gain (Loss), Unrealized	(0.2)	1.8	2.6	(3.2)
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax	0.0	(0.1)	0.0	(0.1)
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax	(0.2)	1.7	2.6	(3.3)
Net unrealized investment gains (losses), pre-tax	25.4	(57.3)	(201.9)	(47.1)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	(9.5)	17.2	24.9	14.6
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	15.9	(40.1)	(177.0)	(32.5)
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	20.7	(13.4)	42.4	(2.0)
Foreign Currency Transaction Gain (Loss), Unrealized	0.0	0.0	0.0	0.0
Net unrealized investment gains (losses), pre-tax	20.7	(13.4)	42.4	(2.0)
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	0.0	0.0	0.0	0.0
Foreign Currency Transaction Gain (Loss), Unrealized	0.0	0.0	0.0	0.0
Net unrealized investment gains (losses), pre-tax	0.0	0.0	0.0	0.0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(10.6)	(22.6)	(260.4)	(25.3)
Foreign Currency Transaction Gain (Loss), Unrealized	0.0	1.6	2.4	(2.4)
Net unrealized investment gains (losses), pre-tax	(10.6)	(21.0)	(258.0)	(27.7)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	15.5	(23.1)	13.5	(16.6)
Foreign Currency Transaction Gain (Loss), Unrealized	(0.2)	0.2	0.2	(0.8)
Net unrealized investment gains (losses), pre-tax	$ 15.3	$ (22.9)	$ 13.7	$ (17.4)

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- Definition

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

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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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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-URI http://asc.fasb.org/extlink&oid=6526789

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