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Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2011 company | Dec. 31, 2012 | Sep. 30, 2012 | Jun. 30, 2012 | Mar. 31, 2012 | Dec. 31, 2011 | Sep. 30, 2011 | Jun. 30, 2011 | Mar. 31, 2011 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of par value of policy reinsured |  | 15.00% |  |  |  |  |  |  |  | 15.00% |  |
Accumulated losses | $ 2,789.7 | $ 2,542.7 |  |  |  | $ 2,789.7 |  |  |  | $ 2,542.7 | $ 2,789.7 |
Noncontrolling interest in VIE | 580.2 | 526.4 |  |  |  | 580.2 |  |  |  | 526.4 | 580.2 |
Non-controlling interest in consolidated subsidiaries |  | 12.0 | 30.9 | (12.1) | (16.8) | (20.3) | 11.0 | (20.8) | (11.4) | (14.0) | 41.5 | 53.0
Number of small manufacturing companies owned by the Tuckerman Fund I from whom the entity received shares | 2 |  |  |  |  |  |  |  |  |  |  |
HG Global |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of par value of policy reinsured |  | 15.00% |  |  |  |  |  |  |  | 15.00% |  |
Noncontrolling interest in VIE | 0 | 16.5 |  |  |  | 0 |  |  |  | 16.5 | 0 |
OneBeacon |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Noncontrolling interest in VIE | 287.2 | 254.2 |  |  |  | 287.2 |  |  |  | 254.2 | 287.2 |
Reciprocals | OneBeacon |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of reciprocals capitalized |  |  |  |  |  |  |  |  |  | 3 |  |
Houston General Insurance |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total assets related to consolidated VIE's | 105.9 | 97.7 |  |  |  | 105.9 |  |  |  | 97.7 | 105.9 |
Total liabilities related to consolidated VIE's | 126.2 | 120.4 |  |  |  | 126.2 |  |  |  | 120.4 | 126.2 |
Houston General Insurance | OneBeacon |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Surplus notes |  | 23.7 |  |  |  |  |  |  |  | 23.7 |  |
Accumulated losses |  | 22.7 |  |  |  |  |  |  |  | 22.7 |  |
Accrued interest on surplus notes |  | 19.7 |  |  |  |  |  |  |  | 19.7 |  |
Prospector Offshore Fund |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total assets related to consolidated VIE's | 135.8 | 151.0 |  |  |  | 135.8 |  |  |  | 151.0 | 135.8 |
Total liabilities related to consolidated VIE's | 31.6 | 51.1 |  |  |  | 31.6 |  |  |  | 51.1 | 31.6 |
Noncontrolling interest in VIE | 38.9 | 28.9 |  |  |  | 38.9 |  |  |  | 28.9 | 38.9 |
Non-controlling interest in consolidated subsidiaries |  |  |  |  |  |  |  |  |  | 2.6 | 0.2 | (3.2)
Ownership interest in VIE (as a percent) |  |  |  |  |  |  |  |  |  | 71.10% |  |
Captial at risk, investment in the fund |  | 71.1 |  |  |  |  |  |  |  | 71.1 |  |
Tuckerman Fund I |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Total assets related to consolidated VIE's | 17.6 |  |  |  |  | 17.6 |  |  |  |  | 17.6 | 19.4
Total liabilities related to consolidated VIE's | 9.9 |  |  |  |  | 9.9 |  |  |  |  | 9.9 | 12.3
Noncontrolling interest in VIE | 3.5 |  |  |  |  | 3.5 |  |  |  |  | 3.5 | 2.4
Non-controlling interest in consolidated subsidiaries |  |  |  |  |  |  |  |  |  |  | 2.2 | 1.0
Entities Owned by Tuckerman Fund I |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of small manufacturing companies owned by the Tuckerman Fund I from whom the entity received shares |  |  |  |  |  |  |  |  |  |  | 2 |
Common shareholders’ equity | BAM |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Issuance of notes |  |  |  |  |  |  |  |  |  | 503.0 |  |
Common shareholders’ equity | Tuckerman Fund I |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest in VIE (as a percent) | 94.00% |  |  |  |  |  |  |  |  |  | 94.00% |
HG Global |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of par value of policy reinsured |  | 15.00% |  |  |  |  |  |  |  | 15.00% |  |
Number of Trust |  | 2 |  |  |  |  |  |  |  | 2 |  |
Surplus notes |  | 503.0 |  |  |  |  |  |  |  | 503.0 |  |
BAM |  |  |  |  |  |  |  |  |  |  |  |
Variable Interest Entity [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of par value of policy reinsured |  | 60.00% |  |  |  |  |  |  |  | 60.00% |  |
Right to elect eirectors on board number |  |  |  |  |  |  |  |  |  | 2 |  |
Surplus notes |  | $ 0 |  |  |  |  |  |  |  | $ 0 |  |

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- Definition Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 5A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7880789&loc=SL6759159-111685 + Details
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- Definition Represents the number of manufacturing companies from whom the entity received the shares. + References No definition available. + Details
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- Definition Number of Trust + References No definition available. + Details
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