Acquisition of Business (Details) - USD ($) $ in Millions			3 Months Ended		6 Months Ended
	May. 07, 2015	Apr. 30, 2015	Sep. 30, 2015	Jun. 30, 2015	Jun. 30, 2015
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		$ 71.0
Insurance Expenses, Impact of Purchase Accounting Adjustments [Line Items]				$ (2.9)	$ (2.9)
Tax Expense, Impact of Purchase Accounting Adjustments				$ 1.0	$ 1.0
Payments to Acquire Businesses, Gross		71.0
Business Combination, Cash Held in Escrow, Indemnification Obligation			$ 17.5
Capital Contribution to Subsidiary	$ 75.0
Goodwill, Purchase Accounting Adjustments			4.5
Business Combination, Indemnification Assets, Amount as of Acquisition Date		5.4
Business Combination, Indemnification Assets			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
Intangible Assets Other Than Intangible Assets Arising from Insurance Contracts Acquired [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		32.6	$ 23.6
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)
Current and Deferred 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