Discontinued Operations - Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	$ 532.6	$ 440.5
Estimate of Fair Value Measurement [Member] | SIG Senior Notes | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	409.0	410.0
Estimate of Fair Value Measurement [Member] | SIG Preference Shares | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	247.5	255.0
Book Value | SIG Senior Notes | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	399.9	399.8
Book Value | SIG Preference Shares | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	$ 250.0	$ 250.0