Acquisition of Business Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	Dec. 31, 2015	Apr. 30, 2015
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		$ 71.0
Business Combination, Indemnification Assets, Amount as of Acquisition Date		5.4
Business Combination, Indemnification Asset	$ 15.9
Investments [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		187.0
Cash [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		13.4
Premiums Receivable [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		44.4
Receivables Other Than Premium Receivables [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		52.8
Finite-Lived Intangible Assets [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	$ 22.0	32.6
Goodwill [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		11.2
Current Income Tax Asset [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		1.4
Other Assets Acquired [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		5.9
Property and Casualty Insurance Reserves [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		155.8
Unearned Premiums [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		85.6
Liabilities for Income Taxes [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		1.5
Other Liabilities [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		34.8
General Indemnification [Member]
Business Acquisition [Line Items]
Business Combination, Indemnification Assets, Range of Outcomes, Value, High		12.5
Employee Related Matters [Member]
Business Acquisition [Line Items]
Business Combination, Indemnification Assets, Range of Outcomes, Value, High		$ 5.0