Other Comprehensive Income (Loss) (Reclassifications out of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	$ (1.1)	$ 3.0
Income (loss) from continuing operations before income taxes	(17.5)	130.0
Loss adjustment expenses and other operating expenses	(1,017.4)	(787.5)
Income tax benefit (expense)	5.5	(24.7)
Income (loss) from continuing operations	(12.0)	105.3
Net income (loss)	(12.0)	104.9
Life [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss from discontinued operations		(0.4)
Reclassification out of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) from sales and other	(1.1)	3.0
Impairments on investments	(10.7)	(0.9)
Income tax benefit (expense)	3.3	(0.4)
Net income (loss)	(10.1)	0.7
Reclassification out of Accumulated Other Comprehensive 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	(2.0)	(1.4)
Income tax benefit (expense)	0.4	0.3
Income (loss) from continuing operations	(1.6)	(1.1)
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Net Unrealized Appreciation (Depreciation) on Investments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before income taxes	(11.8)	2.1
Income (loss) from continuing operations	$ (8.5)	1.7
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Net change in market risk
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss from discontinued operations		0.1
Income tax benefit (expense)		(0.1)
Reclassification out of Accumulated Other Comprehensive Loss [Member] | Net change in market risk | Life [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss from discontinued operations		$ 0.2