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Post-retirement benefit plans - Schedule of allocation plan assets in percentage (Details)
Dec. 31, 2021
Equity securities  
Defined Benefit Plan, Plan Assets, Allocation [Line Items]  
Target allocation (in percentage) 15.00%
Actual allocation (in percentage) 15.00%
Debt securities  
Defined Benefit Plan, Plan Assets, Allocation [Line Items]  
Target allocation (in percentage) 35.00%
Actual allocation (in percentage) 34.00%
Other  
Defined Benefit Plan, Plan Assets, Allocation [Line Items]  
Target allocation (in percentage) 50.00%
Actual allocation (in percentage) 51.00%