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Non-controlling Interest (Details) - USD ($) $ in Millions	Sep. 30, 2016	Aug. 04, 2016	Dec. 31, 2015
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 149.2		$ 454.8
Total Non-Controlling Excluding Reciprocals [Member]
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 36.9		$ 115.2
OneBeacon [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	23.90%		24.50%
Total non-controlling interests	$ 247.0		$ 245.6
SIG Preference Shares
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage			100.00%
Total non-controlling interests	$ 0.0		$ 250.0
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%		3.10%
Total non-controlling interests	$ 16.9		$ 17.1
MediaAlpha [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	40.00%		40.00%
Total non-controlling interests	$ 12.5		$ 14.4
Tranzact [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	0.00%		36.80%
Total non-controlling interests	$ 0.0		$ 79.4
WOBI
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.30%		3.90%
Total non-controlling interests	$ 0.5		$ 0.6
AWG Dewar
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	18.80%		19.00%
Total non-controlling interests	$ 3.7		$ 3.7
Buzzmove [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	29.10%		0.00%
Total non-controlling interests	$ 3.3	$ 2.6	$ 0.0
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%		100.00%
Total non-controlling interests	$ (138.9)		$ (140.0)
Star & Shield Insurance Exchange
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%		100.00%
Total non-controlling interests	$ 4.2		$ (16.0)
Star & Shield Insurance Exchange | Total mutual and reciprocals [Member]
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (134.7)		$ (156.0)

X

- 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

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- Definition

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+ References

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- Definition

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+ References

No definition available.

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