Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended			6 Months Ended	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2014	Dec. 31, 2011
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%								15.00%
Accumulated losses	$ 3,011.4				$ 2,802.3				$ 3,011.4	$ 2,802.3
Noncontrolling interest in VIE	543.0				491.9				543.0	491.9
Non-controlling interest in consolidated subsidiaries	(15.0)	(11.2)	4.6	(0.5)	0.3	(1.1)	(11.1)	(0.5)	(22.1)	(12.4)	(14.0)
Payments to Acquire Other Investments									137.0	36.3	96.7
HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%								15.00%
Noncontrolling interest in VIE	17.9				16.6				17.9	16.6
Star & Shield Insurance Exchange [Member]
Variable Interest Entity [Line Items]
Surplus notes	17.0								17.0
Total assets related to consolidated VIE's	13.5								13.5
Total liabilities related to consolidated VIE's	25.9								25.9
Accumulated losses	12.4								12.4
Prospector
Variable Interest Entity [Line Items]
Total assets related to consolidated VIE's	135.8				249.2				135.8	249.2
Total liabilities related to consolidated VIE's	39.8				90.6				39.8	90.6
Noncontrolling interest in VIE	31.1				46.2				31.1	46.2
Net Income (Loss) Attributable to Parent									5.6	14.5	9.3
Non-controlling interest in consolidated subsidiaries									1.9	4.0	2.7
Captial at risk, investment in the fund	64.9								64.9
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage										67.60%
Houston General Insurance [Member]
Variable Interest Entity [Line Items]
Surplus notes	4.0								4.0
Total assets related to consolidated VIE's	2.4				2.6				2.4	2.6
Total liabilities related to consolidated VIE's	4.0				4.2				4.0	4.2
Accumulated losses	1.8								1.8
Accrued interest on surplus notes	0.2								0.2
TaClaro [Member]
Variable Interest Entity [Line Items]
Payments to Acquire Other Investments	2.0		1.5						3.0
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage									49.00%	27.00%		39.00%
Notes Issued	1.7
Tranzutary Holdings LLC [Member]
Variable Interest Entity [Line Items]
Total assets related to consolidated VIE's	29.6								29.6
Total liabilities related to consolidated VIE's	4.1								4.1
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage									36.00%
Entities Owned by Tuckerman Fund I [Member]
Variable Interest Entity [Line Items]
Number Of Manufacturing Companies From Whom Shares Received								2
Common Stock | BAM
Variable Interest Entity [Line Items]
Issuance of notes										503.0
Common Stock | Tuckerman Fund I [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage													94.00%
BAM
Variable Interest Entity [Line Items]
Right to elect directors on board number										2
HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%								15.00%
Surplus notes	503.0				503.0				503.0	503.0
Noncontrolling interest in VIE	17.9				16.6				17.9	16.6
First Loss Reinsurance Treaty [Member] | HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured	15.00%								15.00%
First Loss Reinsurance Treaty [Member] | BAM
Variable Interest Entity [Line Items]
Percentage of Premiums	60.00%								60.00%
First Loss Reinsurance Treaty [Member] | HG Global
Variable Interest Entity [Line Items]
Number of Trust	2								2
Amendment [Member] | Houston General Insurance [Member]
Variable Interest Entity [Line Items]
Surplus notes	4.0								4.0
Common Stock | TaClaro [Member]
Variable Interest Entity [Line Items]
Stock Issued	0.3
Other Intangible Assets [Member] | Tranzutary Holdings LLC [Member]
Variable Interest Entity [Line Items]
Total assets related to consolidated VIE's	$ 28.9								$ 28.9