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Post-retirement benefits - Summary of main assumptions rate for valuations of plans (Detail)
Dec. 31, 2021
Dec. 31, 2020
Disclosure of defined benefit plans [Line Items]    
Assumption for the consumer price index (%) 2.70% 2.10%
Canada    
Disclosure of defined benefit plans [Line Items]    
Discount rate (%) 2.90% 2.50%
Inflation (%) 1.90% 1.60%
Rate of increase in pensions 0.30% 0.10%
Rate of increase in salaries 3.10% 2.80%
UK    
Disclosure of defined benefit plans [Line Items]    
Discount rate (%) 1.90% 1.20%
Inflation (%) 3.40% 2.90%
Rate of increase in pensions 2.90% 2.50%
Rate of increase in salaries 4.20% 3.60%
US    
Disclosure of defined benefit plans [Line Items]    
Discount rate (%) 2.80% 2.20%
Inflation (%) 2.40% 2.10%
Rate of increase in pensions 0.00% 0.00%
Rate of increase in salaries 3.90% 3.60%
Switzerland    
Disclosure of defined benefit plans [Line Items]    
Discount rate (%) 0.30% 0.10%
Inflation (%) 0.90% 0.90%
Rate of increase in pensions 1.80% 0.50%
Rate of increase in salaries 1.90% 1.90%