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Pension Plans (Fair Value of Plan Assets and Funded Status of Plans) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [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
Interest cost $ 20.5 $ 20.4 $ 21.9  
Qualified Plan [Member]        
Defined Benefit Plan Disclosure [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  
Benefit obligation, beginning of period $ 331.5 $ 348.4    
Interest cost $ 19.2 $ 19.1    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Other Cost and Expense, Operating Other Cost and Expense, Operating    
Actuarial (gains) losses $ 7.4 $ (3.8)    
Benefits paid (31.7) (32.2)    
Benefit obligation, end of year 326.4 331.5 $ 348.4  
Balance at beginning of period 340.4 363.0    
Actual return on plan assets 22.0 9.6    
Benefits paid (31.7) (32.2)    
Balance at end of year 330.7 340.4 $ 363.0  
Funded status of the plans $ 4.3 $ 8.9    
Nonqualified Plan [Member]        
Defined Benefit Plan Disclosure [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  
Benefit obligation, beginning of period $ 21.3 $ 22.6    
Interest cost $ 1.3 $ 1.3    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration] Other Cost and Expense, Operating Other Cost and Expense, Operating    
Actuarial (gains) losses $ 1.1 $ 0.2    
Benefits paid (2.7) (2.8)    
Benefit obligation, end of year 21.0 21.3 $ 22.6  
Contributions 2.7 2.8    
Benefits paid (2.7) (2.8)    
Funded status of the plans $ (21.0) $ (21.3)