Losses and Loss Expenses - Asbestos and Environmental Exposures Claims Rollforward (Details)	12 Months Ended
	Dec. 31, 2014 claims	Dec. 31, 2013 claims	Dec. 31, 2012 claims
Asbestos claims
Reconciliation of opening and closing unpaid losses and loss expenses related to asbestos and environmental exposure claims:
Total number of claims outstanding, beginning of period	1,097	1,073	1,038
New claims reported	456	178	236
Claims resolved	(154)	(154)	(201)
Total number of claims outstanding, end of period	1,399	1,097	1,073
Environmental claims
Reconciliation of opening and closing unpaid losses and loss expenses related to asbestos and environmental exposure claims:
Total number of claims outstanding, beginning of period	338	354	362
New claims reported	190	34	60
Claims resolved	(69)	(50)	(68)
Total number of claims outstanding, end of period	459	338	354