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Investment Securities (Investment Holding Common Equities/ Other Investments) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Common Stock
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	$ 616.6	$ 904.7
Trading Securities, Unrealized Holding Gain	92.6	51.0
Trading Securities, Unrealized Holding Loss	0.0	(30.1)
Net foreign currency gains (losses)	0.0	0.0
Fixed maturity investments, at fair value	709.2	925.6
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	561.9	330.3
Trading Securities, Unrealized Holding Gain	168.2	52.2
Trading Securities, Unrealized Holding Loss	(63.7)	(54.9)
Net foreign currency gains (losses)	(2.0)	(2.0)
Fixed maturity investments, at fair value	$ 664.4	$ 325.6

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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Amount of unrealized holding gain before loss recognized in the income statement for investments in trading securities.

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