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Asset retirement obligations - Rollforward Analysis (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]        
Balance as of January 1     $ 269  
Accretion expense $ 4 $ 3 7 $ 7
Liabilities incurred and acquired     2  
Liabilities settled     (7)  
Foreign currency translation adjustment     2  
Balance as of June 30 $ 273   $ 273