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Benefit Plans - Weighted-Average Asset Allocation of Pension Plan Assets (Detail) - Pension
Dec. 31, 2020
Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]    
Equities 100.00% 100.00%
Domestic equities    
Defined Benefit Plan Disclosure [Line Items]    
Equities 39.00% 37.00%
Foreign equities    
Defined Benefit Plan Disclosure [Line Items]    
Equities 12.00% 11.00%
Fixed income    
Defined Benefit Plan Disclosure [Line Items]    
Equities 47.00% 50.00%
Real estate    
Defined Benefit Plan Disclosure [Line Items]    
Equities 2.00% 2.00%
Cash    
Defined Benefit Plan Disclosure [Line Items]    
Equities 0.00% 0.00%