Document and Entity Information	3 Months Ended
	Mar. 31, 2014	Apr. 24, 2014 Class A common	Apr. 24, 2014 Class B common
Entity Registrant Name	OneBeacon Insurance Group, Ltd.
Entity Central Index Key	0001369817
Document Type	10-Q
Document Period End Date	Mar. 31, 2014
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		23,541,649	71,754,738
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	Q1