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Taxes - Effective tax rate (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Taxes    
Effective tax rate (as a percent) (29.30%) 42.60%
Assets held for sale impairment $ 360  
Devaluation of Mexican peso against U.S. dollar (as a percent) 3.00% 24.00%