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Investment Securities (Other long-term investments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Payments to Acquire Other Investments	$ 22.4	$ 10.9
Other Investments	(331.7)		$ (323.3)
Forward Contracts
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	(4.2)		(1.2)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	(1.3)		(3.2)
Hedge and private equity funds included in other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	(147.2)		(131.0)
Limited liability companies and private equity securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	(72.4)		(72.0)
Surplus Note
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	(69.6)		(71.9)
Convertible Preferred Stock
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	(30.7)		(30.6)
Affordable Housing Development Fund
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	(11.7)	$ (14.1)	(12.3)	$ (14.7)
Partnership investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	(3.0)		(3.5)
Hedge Funds Equity R E I T [Member] | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	19.7		19.9
Unfunded Commitments	$ 0.0		$ 0.0
OneTitle [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Ownership interest (as a percent)	20.00%
Surplus Notes	$ 10.0

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
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-Section 50
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+ References

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Amount of investments classified as other.

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Financial instruments issued by insurance entities (surplus notes) that are includable in surplus for statutory accounting purposes as prescribed or permitted by state laws and regulations that are liabilities of the issuer.

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Amount of other investments classified as trading.

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