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Employee Bargaining Agreements and Benefit Plans - Assumption Rates Used for Benefit Obligations (Detail)
Dec. 31, 2019
Dec. 31, 2018
Minimum [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate: 2.00% 2.65%
Maximum [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate: 2.10% 2.90%