Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended		48 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015
Discontinued Operations [Line Items}
Net gain on sale of discontinued operations	$ 10.3		$ 7.0		$ 18.2	$ 9.7
Net income from discontinued operations, net of tax	3.9		56.9		73.3	166.8
Net Realized and Unrealized Gain (Loss) on Trading Securities	(43.9)		(27.5)		(33.9)	64.4
Sirius Group
Discontinued Operations [Line Items}
Investment Income, Net	5.5		0.9		1.4	1.8
Net Realized and Unrealized Gain (Loss) on Trading Securities	5.5		0.9		1.4	1.8
OneBeacon Runoff [Member]
Discontinued Operations [Line Items}
Change in seller financing				$ 6.7
Amount of Seller Financing				80.9
Surplus Notes				80.9
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
Reserve charge under the SPA, before tax				7.4
Transfer of assets				7.4
Reserve Charge After-Tax				$ 4.8
Proceeds from Sale of Buildings		$ 58.0
Esurance
Discontinued Operations [Line Items}
Net gain on sale of discontinued operations						$ 3.2
Net income from discontinued operations, net of tax	$ 10.3				$ 18.2
Fireman's Fund Insurance Company [Member]
Discontinued Operations [Line Items}
Net gain on sale of discontinued operations			$ 14.0