Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Dec. 31, 2011
Income Tax Contingency [Line Items]
Deferred tax liability	$ 399.7	$ 399.7	$ 365.5
Deferred Income Tax Assets	555.0	555.0	536.9
Effective tax rates (as a percent)	35.40%	27.20%
U.S. statutory rate (as a percent)	35.00%	35.00%
Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions		11.5
Foreign tax credit carryforwards	20.6	20.6
Sweden proposed corporate income tax rate		22.00%
Sweden corporate income tax rate		26.30%
Sirius Group Segment [Member]
Income Tax Contingency [Line Items]
Deferred tax liability	60.0	60.0
Deferred Income Tax Assets	$ 272.1	$ 272.1