Pension Plans (Summary of Plan Assets Investment Measured At Fair Value) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
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	$ 49.2	$ 71.7
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	14.4	16.0	$ 19.1
Fixed Maturities [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	42.7	64.5
Money Market Funds [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	6.5	7.2
Level 1 [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	34.8	55.7
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	28.3	48.5
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	6.5	7.2
Level 3 [Member] | Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Invested assets, fair value	14.4	16.0
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	$ 14.4	$ 16.0