Contingencies (Details) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended		48 Months Ended
	Jun. 30, 2007 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Jan. 22, 2015	Oct. 07, 2011
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		$ 10.3	$ 7.0		$ 18.2	$ 9.7
Esurance
Loss Contingencies [Line Items]
Percentage of fluctuation in loss reserves of transferred subsidiaries retained									90.00%
Tribune Company Litigation | Pending Litigation | OneBeacon
Loss Contingencies [Line Items]
Proceeds from Sale, Maturity and Collection of Investments	$ 32.0
Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		3.9	56.9	$ 2.7	73.3	166.8
OneBeacon Runoff [Member]
Loss Contingencies [Line Items]
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax		10.3	10.3	8.2	18.2		$ 28.3
Net gain on sale of discontinued operations			6.7	$ 5.3
Number of insurance holders								3
OneBeacon Runoff [Member] | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		0.0	(7.0)		0.3	(7.5)
Sirius Group | Tribune Company Litigation | Pending Litigation
Loss Contingencies [Line Items]
Proceeds from Sale, Maturity and Collection of Investments	$ 6.1
Sirius Group | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		$ 4.0	$ 57.2		$ 73.7	$ 167.7