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Deferred tax assets and liabilities - Additional information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]      
Unremitted earnings retained for reinvestment $ 7,000,000,000    
Temporary differences and unused tax losses for which no deferred tax assets were recognized 9,000,000,000 $ 9,000,000,000  
Tax loss carryforwards capitalized 921,000,000 521,000,000  
Tax loss carryforwards expiring in five years 5,000,000    
Expiring in greater than five years or with indefinite carryforward period 916,000,000    
Amount with indefinite carryforward period 559,000,000    
Expiring in 6 to 20 years 357,000,000    
Tax loss carryforwards expired in period $ 0 0 $ 0
Switzerland [member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]      
Deferred tax expense (income) relating to tax rate changes or imposition of new taxes   $ 304,000,000