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Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended |  |  | 3 Months Ended |  | 3 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2014 | Mar. 31, 2013 | Dec. 31, 2013 | Dec. 31, 2012 | Mar. 31, 2014 Segment, Discontinued Operations | Mar. 31, 2013 Segment, Discontinued Operations | Dec. 31, 2013 Segment, Discontinued Operations | Mar. 31, 2014 Segment, Discontinued Operations OneBeacon Runoff Contract | May 31, 2001 N I C O Cover [Member] Segment, Discontinued Operations OneBeacon Runoff | May 31, 2001 G R C Cover [Member] Segment, Discontinued Operations OneBeacon Runoff | Mar. 31, 2014 GRC and NICO Cover [Member] Segment, Discontinued Operations OneBeacon Runoff | Dec. 31, 2013 GRC and NICO Cover [Member] Segment, Discontinued Operations OneBeacon Runoff
Discontinued Operations [Line Items} |  |  |  |  |  |  |  |  |  |  |  |
Loss and loss adjustment expense reserves | $ 3,048.4 | $ 3,100.6 | $ 3,079.3 | $ 3,168.9 | $ 1,717.3 |  | $ 1,793.1 |  |  |  |  |
Net (loss) income from discontinued operations, net of tax | (0.5) | 0.5 |  |  | (0.5) | 0.5 |  |  |  |  |  |
Number of contracts seller caused one beacon to purchase prior to acquisition |  |  |  |  |  |  |  | 2 |  |  |  |
Reinsurance recoverable cover under reinsurance contract |  |  |  |  |  |  |  |  | 2,500.0 | 570.0 |  |
Adverse loss reserve development on losses occurring in years 2000 and prior |  |  |  |  |  |  |  |  |  | 400.0 |  |
Loss reserves ceded at acquisition |  |  |  |  |  |  |  |  |  | 170.0 |  |
Reinsurance recoverables |  |  |  |  |  |  |  |  |  |  | 1,188.8 | 1,243.7
A M Best Rating System, Number of Debt Ratings |  |  |  |  |  |  |  | 16 |  |  |  |
Reinsurance recoverable on paid losses |  |  |  |  |  |  |  | 9.5 |  |  |  |
Reinsurance recoverables, gross of purchase accounting adjustments |  |  |  |  |  |  |  | 1,673.6 |  |  |  |
Purchase accounting adjustments |  |  |  |  |  |  |  | $ 133.6 |  |  |  |

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- Definition Amount of income (loss) from a disposal group, net of income tax before extraordinary items allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e957-107759 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.12) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 13 -Article 7 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.14) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Article 5 + Details
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- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a),(b),(c) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 + Details
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- Definition Amount after valuation allowance currently billed or billable under reinsurance contracts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21412-158489 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21409-158489 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.6) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 6 -Article 7 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
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- Definition Amount after valuation allowance recoverable including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 6 -Article 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.(a),6) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition Amount before valuation allowance recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves. + References No definition available. + Details
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- Definition Represents the amount of adverse loss reserve development on losses occurring in years 2000 and prior. + References No definition available. + Details
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- Definition Represents the number of reinsurance contracts the seller caused subsidiary entity to purchase from subsidiaries of Berkshire Hathaway Inc. immediately prior to the entity's acquisition of subsidiary entity. + References No definition available. + Details
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- Definition Reinsurance recoverables gross of purchase accounting adjustments. + References No definition available. + Details
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- Definition Purchase accounting adjustments related to reinsurance recoverables. + References No definition available. + Details
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