Discontinued Operations - Interest Rate Cap (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended			6 Months Ended	9 Months Ended
	Jul. 31, 2013	May. 31, 2007	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Preferred Stock [Member] | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Preferred Stock, Dividend Rate, Percentage		7.506%
Interest Rate Cap [Member] | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Years of interest rate cap					5 years
Derivative, Cap Interest Rate	8.30%
Derivative, Cost of Hedge	$ 9.9
Beginning of period			$ 3.3	$ 6.2		$ 4.1	$ 4.1	$ 11.1
Realized and unrealized gains (losses)			(1.1)	(0.8)			(1.9)	(5.7)
End of period			$ 2.2	$ 5.4		$ 3.3	$ 2.2	$ 5.4
Interest Rate Cap [Member] | Preferred Stock [Member] | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale of Stock, Number of Shares Issued in Transaction	250,000,000.0
Sirius Group Ltd [Member] | Preferred Stock [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Term of LIBOR loan		3 months
Basis points		3.20%
Sirius Group Ltd [Member] | Interest Rate Cap [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Basis points	3.95%