Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	$ (19.2)	$ 4.8	$ (16.2)	$ 3.2
Income from continuing operations before income taxes	28.2	159.9	158.2	274.0
Loss adjustment expenses and other operating expenses	(845.5)	(745.1)	(1,633.0)	(1,526.4)
Income tax benefit (expense)	(5.4)	(30.3)	(30.1)	(51.6)
Income from continuing operations	22.8	129.6	128.1	222.4
Net income	22.6	128.5	127.4	221.2
Life [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Discontinued operations - loss from discontinued life businesses	(0.2)	(1.1)	(0.7)	(1.2)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	(19.7)	4.8	(16.7)	3.2
Recoveries (impairments) on investments	(1.5)	(0.2)	(2.4)	(0.2)
Income tax benefit (expense)	(5.2)		(4.8)	(2.2)
Net income	(17.0)	3.9	(16.4)	3.8
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	(1.3)	(0.9)	(2.7)	(1.7)
Income tax benefit (expense)	0.2	0.2	0.5	0.3
Income from continuing operations	(1.1)	(0.7)	(2.2)	(1.4)
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]
Income from continuing operations before income taxes	(21.2)	4.6	(19.1)	3.0
Income from continuing operations	(16.0)	4.6	(14.3)	5.2
Net income	(15.9)	$ 4.6	(14.2)	$ 5.2
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 - loss from discontinued life businesses	$ 0.1		$ 0.1