Pension Plans (Summary of Plan Assets Investment Measured At Fair Value) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Defined Benefit Plan, Type [Extensible List]	us-gaap:PensionPlansDefinedBenefitMember	us-gaap:PensionPlansDefinedBenefitMember	us-gaap:PensionPlansDefinedBenefitMember
Defined Benefit Plan, Sponsor Location [Extensible List]	us-gaap:DomesticPlanMember	us-gaap:DomesticPlanMember	us-gaap:DomesticPlanMember
Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	$ 40.9	$ 49.2
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	12.3	14.4	$ 16.0
Fixed Maturities [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	34.6	42.7
Money Market Funds [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	6.3	6.5
Level 1 [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	28.6	34.8
Level 1 [Member] | Fixed Maturities [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	22.3	28.3
Level 1 [Member] | Money Market Funds [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	6.3	6.5
Level 3 [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	12.3	14.4
Level 3 [Member] | Fixed Maturities [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	$ 12.3	$ 14.4