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Significant accounting policies (Details)
$ in Billions
 12 Months Ended
Dec. 31, 2020
USD ($)
$ / t
kr / t
Significant accounting policies [Abstract]  
Internal carbon price | $ / t 56
Expected tax increase on carbon emissions minimum | $ / t 590
Expected tax increase on carbon emissions maximum | kr / t 2,000
Expected cost increase from increase in CO2 tax | $ $ 0.4
Reserve for exposure to market risks | $ $ 3.0