Summary of Significant Accounting Policies (Basis of Presentation) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended				3 Months Ended							1 Months Ended	12 Months Ended
	Dec. 31, 2011 company	Dec. 31, 2013 state	Dec. 31, 2012	Dec. 31, 2013 OneBeacon Ltd.	Dec. 31, 2012 OneBeacon Ltd.	Sep. 30, 2012 HG Global	Dec. 31, 2013 HG Global	Dec. 31, 2012 HG Global	Dec. 31, 2013 Redeemable preferred stocks HG Global	Dec. 31, 2012 Redeemable preferred stocks HG Global	Dec. 31, 2013 Common Stock HG Global	Dec. 31, 2012 Common Stock HG Global	Dec. 31, 2011 Tuckerman Fund I Common Stock	Dec. 31, 2011 Tuckerman Fund I Common Stock
Basis of Presentation
Capital contributions						$ 600.0
BAM Surplus notes							$ 503.0	$ 503.0
Ownership interest (as a percent)				75.20%	75.20%		97.30%		97.30%	97.30%	88.70%	88.70%
Percentage of par value of policy reinsured			15.00%				15.00%
Ownership interest in VIE (as a percent)													94.00%	94.00%
Number of manufacturing companies	2
Number of states		30
Workers compensation discount percent		3.50%	3.50%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners				24.80%	24.80%