Business Segments - Segment Information (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) segment	Sep. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments \| segment			2
Earned Premiums	$ 598.2	$ 558.9	$ 1,744.1	$ 1,658.6
Net Investment Income	85.9	77.7	244.6	218.4
Other Income	1.0	0.8	2.9	2.2
Total Revenues	690.3	640.7	2,026.1	1,879.2
Net Realized Gains on Sales of Investments	8.1	11.6	45.0	24.0
Net Impairment Losses Recognized in Earnings	(2.9)	(8.3)	(10.5)	(24.0)
Segment Operating Profit (Loss)	63.1	(36.5)	82.4	(37.1)
Total Before Income Taxes	68.3	(33.2)	116.9	(37.1)
Segment Net Operating Income (Loss)	44.4	(20.4)	61.5	(16.4)
Income (Loss) from Continuing Operations	47.8	(18.3)	84.0	(16.4)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Segment Operating Profit (Loss)	(3.7)	(6.4)	(15.2)	(23.3)
Segment Net Operating Income (Loss)	(2.0)	(3.1)	(9.7)	(13.8)
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Other Income	2.1	2.8	8.4	6.7
Net Realized Gains on Sales of Investments	8.1	11.6	45.0	24.0
Net Impairment Losses Recognized in Earnings	(2.9)	(8.3)	(10.5)	(24.0)
Net Realized Gains (Losses) on Sales of Investments, Net of Tax	5.3	7.5	29.3	15.6
Net Impairment Losses Recognized in Earnings, Net of Tax	(1.9)	(5.4)	(6.8)	(15.6)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	683.0	634.6	1,983.2	1,872.5
Segment Operating Profit (Loss)	66.8	(30.1)	97.6	(13.8)
Income (Loss) from Continuing Operations	46.4	(17.3)	71.2	(2.6)
Operating Segments [Member] \| Property and Casualty Insurance [Member]
Segment Reporting Information [Line Items]
Earned Premiums	443.5	406.9	1,283.1	1,205.7
Net Investment Income	27.8	20.4	72.5	52.0
Other Income	0.4	0.1	0.9	0.4
Total Revenues	471.7	427.4	1,356.5	1,258.1
Segment Operating Profit (Loss)	30.8	15.6	(2.2)	(24.4)
Income (Loss) from Continuing Operations	22.9	12.1	5.7	(9.9)
Operating Segments [Member] \| Life and Health Insurance [Member]
Segment Reporting Information [Line Items]
Earned Premiums	154.7	152.0	461.0	452.9
Net Investment Income	55.9	54.5	163.8	159.6
Other Income	0.7	0.7	1.9	1.9
Total Revenues	211.3	207.2	626.7	614.4
Segment Operating Profit (Loss)	36.0	(45.7)	99.8	10.6
Income (Loss) from Continuing Operations	$ 23.5	$ (29.4)	$ 65.5	$ 7.3

Gain (Loss) on Sale of Investments, Net of Tax

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Operating Income Loss, Net Of Taxes

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Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net of Tax

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This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting.

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Amount after tax of income (loss) from continuing operations attributable to the parent.

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Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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The net result for the period of deducting operating expenses from operating revenues.

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Amount of revenue and income classified as other.

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The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

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Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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