Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended	3 Months Ended					9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Segment, Discontinued Operations	Sep. 30, 2013 Segment, Discontinued Operations	Sep. 30, 2014 Segment, Discontinued Operations	Sep. 30, 2013 Segment, Discontinued Operations	Sep. 30, 2014 Segment, Discontinued Operations OneBeacon Runoff Contract	Jun. 30, 2014 Segment, Discontinued Operations OneBeacon Runoff	Sep. 30, 2014 Segment, Discontinued Operations OneBeacon Runoff Rating Contract	Jun. 30, 2014 OneBeacon Runoff Segment, Discontinued Operations	May 31, 2001 N I C O Cover [Member] Segment, Discontinued Operations OneBeacon Runoff	May 31, 2001 G R C Cover [Member] Segment, Discontinued Operations OneBeacon Runoff	Sep. 30, 2014 GRC and NICO Cover [Member] Segment, Discontinued Operations OneBeacon Runoff	Dec. 31, 2013 GRC and NICO Cover [Member] Segment, Discontinued Operations OneBeacon Runoff	Sep. 30, 2014 Safeco v. American International Group, Inc. [Member] Segment, Discontinued Operations
Discontinued Operations [Line Items}
Net income from discontinued operations					$ 6.7	$ 0.4	$ 8.8	$ 4.8
Net income from discontinued operations, net of tax	6.7	0.4	8.8	4.8	(0.3)	0.4	(0.9)	4.8
Other Income	5.3	18.2	8.3	46.9	0	0.1	0	12.3									7.4
Increase decrease cap of seller financing										6.7
Seller financing										80.9
Surplus Notes										80.9
Discontinued Operation, Estimated Gain (Loss) from Disposal of Discontinued Operation, before Income Tax										8.2
Discontinued Operation, Estimated Gain (Loss) on Disposal of Discontinued Operation, Net of Tax										5.3
Reserve charge under the SPA, before tax												7.4
Reserve charge under the SPA, after-tax												4.8
Number of contracts seller caused one beacon to purchase prior to acquisition									2		2
Reinsurance recoverable cover under reinsurance contract													2,500.0	570.0
Adverse loss reserve development on losses occurring in years 2000 and prior														400.0
Loss reserves ceded at acquisition														170.0
Reinsurance recoverables															1,127.4	1,243.7
A M Best Rating System, Number of Debt Ratings											16
Reinsurance recoverable on paid losses									7.4		7.4
Reinsurance recoverables, gross of purchase accounting adjustments									1,585.4		1,585.4
Purchase accounting adjustments									127.0		127.0
Gain (Loss) on Disposal of Discontinued Operation	14.0				7.0	0	9.7	0	6.7
Transfer of additional assets												7.4
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax									$ 10.3