Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	$ (1.6)	$ 3.1
Income (loss) from continuing operations before income taxes	114.1	(53.9)
Loss adjustment expenses and other operating expenses	(781.3)	(728.2)
Tax benefit	(21.3)	15.2
Income (loss) from continuing operations	92.8	(38.7)
Net income (loss)	92.7	(40.0)
Life [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Discontinued operations - life businesses	(0.1)	(1.3)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(0.1)	(14.8)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Defined Benefit Pension and Postretirement Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss adjustment expenses and other operating expenses	(0.8)	(1.5)
Tax benefit	0.1	0.3
Income (loss) from continuing operations	(0.7)	(1.2)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Unrealized Appreciation (Depreciation) on Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	(1.6)	3.1
Impairment losses on investments		(22.2)
Income (loss) from continuing operations before income taxes	(1.6)	(19.1)
Tax benefit	2.2	5.9
Income (loss) from continuing operations	0.6	(13.2)
Net income (loss)	$ 0.6	(13.6)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Unrealized Appreciation (Depreciation) on Investments [Member] | Life [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Discontinued operations - life businesses		$ (0.4)