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Post-Employment and Other Non-Current Employee Benefits - Balances of Liabilities for Summary of Variable Return Financial Instruments Recorded at Market Values (Detail)
Dec. 31, 2020
Dec. 31, 2019
Variable return:    
Fixed and variable trust assets 100.00% 100.00%
Traded securities    
Fixed return:    
Fixed return 18.00% 18.00%
Life annuities    
Fixed return:    
Fixed return 18.00% 20.00%
Bank instruments    
Fixed return:    
Fixed return 17.00% 9.00%
Federal government instruments    
Fixed return:    
Fixed return 27.00% 35.00%
Publicly traded shares    
Variable return:    
Variable return 20.00% 18.00%