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Deferred tax assets and liabilities - Additional information (Details) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
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 521,000,000 146,000,000  
Tax loss carryforwards expiring in five years 33,000,000    
Tax loss carryforwards expiring in more than five years 488,000,000    
Tax loss carryforwards expired in period 0 0 $ 0
Deferred tax expense (income) relating to tax rate changes or imposition of new taxes 0 $ 0 (413,000,000)
Income statement [member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]      
Revaluation of deferred tax assets and liabilities and current income tax liabilities     413,000,000
Equity statement [member]      
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]      
Revaluation of deferred tax assets and liabilities and current income tax liabilities     $ 18,000,000
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