SCHEDULE IV REINSURANCE (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Premiums earned
Gross amount	$ 1,433.7
Ceded to other companies	(371.1)
Assumed from other companies	996.3
Net earned premiums	2,058.9	1,987.3	2,063.6
OneBeacon
Premiums earned
Gross amount	1,209.1	1,043.3	1,158.3
Ceded to other companies	(102.9)	(71.4)	(79.1)
Assumed from other companies	70.9	148.5	52.8
Net earned premiums	1,177.1	1,120.4	1,132.0
Percentage of amount assumed to net	6.00%	13.30%	4.70%
Sirius Group
Premiums earned
Gross amount	200.2	174.0	169.9
Ceded to other companies	(251.7)	(246.2)	(226.6)
Assumed from other companies	925.4	938.6	988.3
Net earned premiums	873.9	866.4	931.6
Percentage of amount assumed to net	105.90%	108.30%	106.10%
HG/BAM
Premiums earned
Gross amount	1.8
Ceded to other companies	0
Assumed from other companies	0
Net earned premiums	1.8
Percentage of amount assumed to net	0.00%
Other Segments
Premiums earned
Gross amount	22.6
Ceded to other companies	(16.5)
Assumed from other companies	0
Net earned premiums	$ 6.1	$ 0	$ 0
Percentage of amount assumed to net	0.00%