Derivatives (Interest rate cap) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		1 Months Ended		3 Months Ended
	Mar. 31, 2015 Rating	Mar. 31, 2014	May 31, 2007	Jul. 31, 2013	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013
Interest Rate Cap
Derivative [Line Items]
Derivative collateral right to reclaim	$ 3.1
Derivative, fair value, net	3.1	8.2				4.1	11.1
Realized and unrealized gains (losses)	(1.0)	(2.9)
S and P Credit Ratings	23
Sirius International Group Ltd | Preferred Stock
Derivative [Line Items]
Preferred Stock, Dividend Rate, Percentage			7.506%
Term of LIBOR loan			3 months
Basis points			3.20%
Sirius International Group Ltd | Interest Rate Cap
Derivative [Line Items]
Derivative, Cap Interest Rate							8.30%
Derivative, Cost of Hedge				9.9
Basis points	3.95%
years of interest rate cap					5 years
Sirius International Group Ltd | Interest Rate Cap | Preferred Stock
Derivative [Line Items]
Non-cumulative perpetual preference shares issued			250,000,000
Standard & Poor's, A Rating | Barclays | Interest Rate Cap
Derivative [Line Items]
Derivative collateral right to reclaim	2.1
Standard & Poor's, AA- Rating | Nordea Bank Finland | Interest Rate Cap
Derivative [Line Items]
Derivative collateral right to reclaim	$ 1.0