Derivatives (Interest rate cap) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended			1 Months Ended	6 Months Ended
	Jun. 30, 2014 Interest Rate Cap Rating	Jun. 30, 2014 Interest Rate Cap Rating	Mar. 31, 2014 Interest Rate Cap	Dec. 31, 2013 Interest Rate Cap	May 31, 2007 Sirius International Group Ltd Preferred Stock	Jun. 30, 2014 Sirius International Group Ltd Interest Rate Cap	Jun. 30, 2014 Standard & Poor's, A Rating Barclays Interest Rate Cap	Jun. 30, 2014 Standard & Poor's, AA- Rating Nordea Bank Finland Interest Rate Cap
Derivative [Line Items]
Derivative collateral right to reclaim	$ 6.3	$ 6.3					$ 4.3	$ 2.0
Preferred Stock, Dividend Rate, Percentage					7.506%
Term of LIBOR loan					3 months
Derivative, Cap Interest Rate						8.30%
Derivative, Cost of Hedge						9.9
basis points					3.20%	3.95%
Non-cumulative perpetual preference shares issued					250.0
years of interest rate cap						5 years
Derivative, fair value, net	6.2	6.2	8.2	11.1
Realized and unrealized gains (losses)	$ (2.0)	$ (4.9)
S and P Credit Ratings	21	21