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Non-controlling Interest (Details) - USD ($) $ in Millions | Sep. 30, 2015 | Dec. 31, 2014
--- | --- | ---
Noncontrolling Interest [Line Items] |  |
Total non-controlling interests | $ 460.8 | $ 542.7
Total Non-Controlling Excluding Reciprocals [Member] |  |
Noncontrolling Interest [Line Items] |  |
Total non-controlling interests | $ 113.3 | $ 168.6
OneBeacon |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 24.70% | 24.70%
Total non-controlling interests | $ 246.9 | $ 258.4
SIG Preference Shares |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 100.00% | 100.00%
Total non-controlling interests | $ 250.0 | $ 250.0
HG Global |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 3.10% | 3.10%
Total non-controlling interests | $ 17.3 | $ 17.9
MediaAlpha |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 40.00% | 40.00%
Total non-controlling interests | $ 15.1 | $ 22.6
Tranzact [Member] |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 36.80% | 36.80%
Total non-controlling interests | $ 75.6 | $ 88.2
WOBI |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 4.70% | 36.70%
Total non-controlling interests | $ 1.8 | $ 5.4
Prospector Offshore Fund Ltd [Member] |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 0.00% | 23.40%
Total non-controlling interests | $ 0.0 | $ 31.1
A W G Dewar Inc [Member] |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 32.20% | 18.00%
Total non-controlling interests | $ 3.5 | $ 3.4
Build America Mutual |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 100.00% | 100.00%
Total non-controlling interests | $ (134.2) | $ (121.9)
Star & Shield Insurance Exchange |  |
Noncontrolling Interest [Line Items] |  |
Noncontrolling equity percentage | 100.00% | 100.00%
Total non-controlling interests | $ (15.2) | $ (12.4)

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- Definition Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.31) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 27 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 20 -Article 7 + Details
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