Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended		60 Months Ended
	Jun. 30, 2007	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Oct. 07, 2011
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations					$ 414.5	$ 18.2
Esurance
Loss Contingencies [Line Items]
Percentage of fluctuation in loss reserves of transferred subsidiaries retained								90.00%
Tribune Company Litigation | Pending Litigation | OneBeacon [Member]
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		$ 14.0		$ (3.8)	7.1	59.1
Esurance
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations				10.3		18.2
Esurance | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		10.3		10.3		17.9	$ 28.3
OneBeacon Runoff [Member] | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations						0.3
Sirius Group
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		$ (4.0)	$ 366.6	0.0	362.6	0.0
Sirius Group | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations			$ 0.0	$ 4.0	$ (6.4)	$ 73.7