Goodwill and Other Intangible Assets (Goodwill and Intangible Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Oct. 10, 2014	Mar. 14, 2014	Feb. 19, 2014	Dec. 31, 2013
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 232.3	$ 198.3
Amortization of Intangible Assets	44.5	16.0
Intangible Assets, Net (Excluding Goodwill)	187.8	182.3				$ 5.1
Goodwill	187.9	168.9				$ 0.0
Intangible Assets, Gross (Including Goodwill)	420.2	367.2
Goodwill and intangible assets	375.7	351.2
Tranzact [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	177.5	146.3
Amortization of Intangible Assets	21.4	3.5
Intangible Assets, Net (Excluding Goodwill)	156.1	142.8	$ 146.3
Goodwill	163.8	145.1	$ 145.1
MediaAlpha
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	38.5	38.5
Amortization of Intangible Assets	14.1	6.0
Intangible Assets, Net (Excluding Goodwill)	24.4	32.5		$ 38.5
Goodwill	18.3	18.3		$ 18.3
WOBI [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	5.7	2.9
Amortization of Intangible Assets	1.2	0.4
Intangible Assets, Net (Excluding Goodwill)	4.5	2.5
Goodwill	5.8	5.5			$ 5.5
Developed Technology Rights [Member] | Tranzact [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	12.7	12.7
Amortization of Intangible Assets	2.8	0.5
Intangible Assets, Net (Excluding Goodwill)	$ 9.9	12.2
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	6 years
Developed Technology Rights [Member] | MediaAlpha
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 32.0	32.0
Amortization of Intangible Assets	11.2	4.8
Intangible Assets, Net (Excluding Goodwill)	$ 20.8	27.2
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years
Developed Technology Rights [Member] | WOBI [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 3.6	0.8
Amortization of Intangible Assets	0.7	0.2
Intangible Assets, Net (Excluding Goodwill)	$ 2.9	0.6
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years
Customer Relationships [Member] | Tranzact [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 132.3	107.5
Amortization of Intangible Assets	13.1	2.1
Intangible Assets, Net (Excluding Goodwill)	$ 119.2	105.4
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	11 years
Customer Relationships [Member] | MediaAlpha
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 6.5	6.5
Amortization of Intangible Assets	2.9	1.2
Intangible Assets, Net (Excluding Goodwill)	$ 3.6	5.3
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	4 years
Customer Relationships [Member] | Star & Shield LLC [Member]
Goodwill [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	3 years
Customer Relationships [Member] | Star & Shield Insurance Exchange [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 1.2	1.2
Amortization of Intangible Assets	0.8	0.4
Intangible Assets, Net (Excluding Goodwill)	0.4	0.8
Trademarks [Member] | WOBI [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	2.1	2.1
Amortization of Intangible Assets	0.5	0.2
Intangible Assets, Net (Excluding Goodwill)	$ 1.6	1.9
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	8 years
Other Intangible Assets [Member] | Tranzact [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 2.0	0.5
Amortization of Intangible Assets	0.1	0.0
Intangible Assets, Net (Excluding Goodwill)	$ 1.9	0.5
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	8 years
Other Intangible Assets [Member] | OneBeacon
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 9.4	9.4
Amortization of Intangible Assets	7.0	5.7
Intangible Assets, Net (Excluding Goodwill)	$ 2.4	3.7
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	10 years
Trade Names [Member] | Tranzact [Member]
Goodwill [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 30.5	25.6
Amortization of Intangible Assets	5.4	0.9
Intangible Assets, Net (Excluding Goodwill)	$ 25.1	$ 24.7
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	7 years