Derivatives (Forward Contract Collateral) (Details) - Sirius Group SEK in Millions, $ in Millions	Jun. 30, 2015 USD ($) Rating	Jun. 30, 2015 SEK Rating	Dec. 31, 2014 USD ($)
Forward Contracts
Derivative [Line Items]
Notional amount	$ 31.9	SEK 262.7	$ 33.1
Carrying Value	$ (0.2)		0.0
S and P Credit Ratings | Rating	23	23
Interest Rate Cap
Derivative [Line Items]
S and P Credit Ratings | Rating	23	23
Standard & Poor's, A- Rating | Forward Contracts | Barclays
Derivative [Line Items]
Notional amount	$ 0.8		2.1
Carrying Value	0.0		0.0
Standard & Poor's, BBB plus Rating | Forward Contracts | Deutsche Bank
Derivative [Line Items]
Notional amount	8.5		0.0
Carrying Value	0.0		0.0
A | Forward Contracts | JP Morgan
Derivative [Line Items]
Notional amount	1.2		5.7
Carrying Value	0.0		0.0
Standard & Poor's, AA- Rating | Forward Contracts | Goldman Sachs
Derivative [Line Items]
Notional amount	5.0		8.7
Carrying Value	(0.1)		0.0
Standard & Poor's, AA- Rating | Forward Contracts | HSBC
Derivative [Line Items]
Notional amount	12.0		11.2
Carrying Value	(0.1)		0.0
Standard & Poor's, AA- Rating | Forward Contracts | Royal Bank of Canada
Derivative [Line Items]
Notional amount	4.4		5.4
Carrying Value	$ 0.0		$ 0.0