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Assumptions Used to Determine Benefit Obligations (Detail)
Dec. 31, 2019
Dec. 31, 2018
Pension benefits    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 3.10% 3.90%
Long-term rate of compensation increase 4.50% 4.50%
Other postretirement benefits    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 3.10% 3.90%
Long-term rate of compensation increase 4.50% 4.50%