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Pension Plans (Summary for Assets Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring 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 us-gaap:DomesticPlanMember
Fixed Maturities [Member]        
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]        
Balance at beginning of period $ 10.8 $ 12.3    
Less: Assets transferred to Level 1 investments (2.4) (1.9)    
Interest earned on plan assets held 0.3 0.4    
Balance at end of year $ 8.7 $ 10.8 $ 12.3