Other Comprehensive Loss (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	$ (0.1)	$ 3.6	$ (16.3)	$ 6.8
Income from continuing operations before income taxes	0.5	42.5	158.7	316.5
Loss adjustment expenses and other operating expenses	(939.6)	(844.0)	(2,572.6)	(2,370.4)
Income tax benefit	0.1	(7.7)	(30.0)	(59.3)
Income from continuing operations	0.6	34.8	128.7	257.2
Net income	0.2	34.0	127.6	255.2
Life [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Discontinued operations - loss from discontinued life businesses	(0.4)	(0.8)	(1.1)	(2.0)
Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other		2.5	(16.7)	5.7
Recoveries (impairments) on investments	(15.7)	0.1	(18.1)	(0.1)
Income tax benefit	3.6	0.3	8.4	2.5
Net income	(13.5)	2.3	(29.9)	6.1
Reclassification out of Accumulated Other Comprehensive Income (Loss) [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	(1.4)	(0.8)	(4.1)	(2.5)
Income tax benefit	0.3	0.2	0.8	0.5
Income from continuing operations	(1.1)	(0.6)	(3.3)	(2.0)
Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member] | Net Unrealized Appreciation (Depreciation) on Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income from continuing operations before income taxes	(15.7)	2.6	(34.8)	5.6
Income from continuing operations	(12.1)	2.9	(26.4)	8.1
Net income	(12.4)	$ 2.9	(26.6)	$ 8.1
Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member] | Net Unrealized Appreciation (Depreciation) on Investments [Member] | Life [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Discontinued operations - loss from discontinued life businesses	$ (0.3)		$ (0.2)