SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS
Rate at which reserves are discounted (as a percent)	2.50%	3.50%	3.50%
OneBeacon
SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS
Deferred acquisition costs	$ 103.2	$ 103.7	$ 123.9
Reserves for Unpaid Claims and Claims Adjustment Expenses	1,342.2	1,054.3	1,000.0
Discount, if any, deducted in Column C	1.0	3.0	4.6
Unearned Premiums	588.3	544.9	573.8
Earned Premiums	1,177.1	1,120.4	1,132.0
Net investment income	41.7	41.1	53.6
Claims and ClaimsAdjustment ExpensesIncurred Related to, Current Year	725.3	622.1	657.4
Claims and ClaimsAdjustment ExpensesIncurred Related to, Prior Year	89.8	0	(7.4)
Amortization of deferred policy acquisition	203.3	208.9	249.4
Paid Claims and Claims Adjustment Expenses	608.6	540.7	565.1
Premiums written	1,216.9	1,088.6	1,179.2
Sirius Group
SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS
Deferred acquisition costs	69.9	69.3	71.4
Reserves for Unpaid Claims and Claims Adjustment Expenses	1,809.8	2,025.0	2,168.9
Discount, if any, deducted in Column C	0.7	1.7	2.4
Unearned Premiums	338.6	343.3	350.2
Earned Premiums	873.9	866.4	931.6
Net investment income	41.1	30.3	65.0
Claims and ClaimsAdjustment ExpensesIncurred Related to, Current Year	443.2	466.8	578.4
Claims and ClaimsAdjustment ExpensesIncurred Related to, Prior Year	(98.0)	(48.4)	(34.5)
Amortization of deferred policy acquisition	193.6	166.5	180.8
Paid Claims and Claims Adjustment Expenses	544.9	628.1	741.2
Premiums written	882.5	876.6	947.7
Other Operations
SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS
Deferred acquisition costs	0	0	0
Reserves for Unpaid Claims and Claims Adjustment Expenses	7.8	0	0
Discount, if any, deducted in Column C	0	0	0
Unearned Premiums	0	0	0
Earned Premiums	0.8	0	0
Net investment income	0.2	0	0
Claims and ClaimsAdjustment ExpensesIncurred Related to, Current Year	6.7	0	0
Claims and ClaimsAdjustment ExpensesIncurred Related to, Prior Year	2.2	0	0
Amortization of deferred policy acquisition	0	0	0
Paid Claims and Claims Adjustment Expenses	14.8	0	0
Premiums written	$ 5.9	$ 0	$ 0

Amount of amortization expense on deferred policy acquisition cost.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 235

-Section S99

-Paragraph 3

-Subparagraph (SX 210.12-18)

-URI http://asc.fasb.org/extlink&oid=6588446&loc=d3e575016-122915

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 18

-Article 12

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Amount of insurance benefit, claims, loss and settlement expenses paid to the policyholders during the current accounting period.

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Amount of deferred policy acquisition cost related to property-casualty insurance policy written.

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The amount of discount that may be deducted from the reserve for unpaid claims and claims adjustment expense.

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Amount of property-casualty insurance premium revenue earned on insurance policies.

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The rate at which the discount was computed for each business segment reported.

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Amount of net investment income earned by property-casualty insurance underwriter.

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Payments of claims and claims adjustment expenses during the period of a property-casualty insurance entity.

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Amount of actual premium written by property-casualty insurance underwriter.

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Amount of insurance benefit, claims, loss and settlement expenses paid to the policyholders during the prior accounting period.

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The amount of reserve, policy claim payable and loss expense incurred by property-casualty insurance underwriter.

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Amount of property-casualty insurance premium revenue not yet earned on insurance policies.

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