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Commitments and Contingencies (Legal Contingencies) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2007	Dec. 31, 2016
OneBeacon | Pending Litigation [Member] | Tribune Company Litigation [Member]
Loss Contingencies [Line Items]
Proceeds From Tribune Common Stock	$ 32.0
OneTitle [Member]
Loss Contingencies [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest		20.00%
Surplus notes		$ 10.0
Sirius Group | Pending Litigation [Member] | Tribune Company Litigation [Member]
Loss Contingencies [Line Items]
Proceeds From Tribune Common Stock	$ 6.1

X

- Definition

Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

Financial instruments issued by insurance entities (surplus notes) that are includable in surplus for statutory accounting purposes as prescribed or permitted by state laws and regulations that are liabilities of the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6486086&loc=d3e24387-158525

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- Definition

Proceeds from Tribune common stock tendered in connecttion with Tribune's leveraged buyout.

+ References

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