Variable Interest Entities (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]
Income Tax Expense (Benefit)	$ (44,400,000)	$ (13,000,000.0)	$ (87,000,000.0)	$ (64,800,000)
Other Assets	488,700,000		488,700,000		$ 530,000,000.0
Surplus Notes and Guarantee Fund Certificates, Reciprocal Exchange			4,000,000
Variable Interest Entity, Not Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Variable Interest Entity, Funding Investment Commitment, Funding	0	0	0	0
Proceeds from Equity Method Investment, Distribution	500,000	600,000	1,500,000	1,500,000
Income (Loss) from Equity Method Investments	800,000	400,000	2,300,000	(21,200,000)
Income Tax Credits and Adjustments	0	0	(100,000)	3,900,000
Income Tax Expense (Benefit)	(200,000)	$ (100,000)	(500,000)	$ 4,100,000
Cash and Cash Equivalents, at Carrying Value	2,800,000		2,800,000		3,000,000.0
Property, Plant and Equipment, Net	256,600,000		256,600,000		261,700,000
Other Assets	6,900,000		6,900,000		5,100,000
Assets	266,400,000		266,400,000		269,700,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 17,200,000		$ 17,200,000		$ 16,300,000