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Shareholders' equity - Narrative (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Jun. 30, 2019
Dec. 31, 2018
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Authorized shares of common stock (shares) 3,500,000,000   3,500,000,000  
Common stock, par value (usd per share) $ 0.01   $ 0.01  
Common stock, shares, outstanding (shares) 900,683,038      
Additional shares authorized to be repurchased     $ 830,000,000  
Treasury stock acquired (shares) 69,300,000      
Treasury stock acquired, average cost per share (usd per share) $ 48.01      
Shares repurchased during period, value $ 3,300,000,000      
Stock repurchase program, remaining authorized repurchase amount $ 1,900,000,000      
Preferred stock, shares authorized (shares) 100,000,000   100,000,000  
Preferred stock, par value (usd per share) $ 0.01   $ 0.01  
Temporary equity $ 143,000,000   $ 129,000,000  
A2017 Capital Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Authorized amount of shares to repurchase       $ 2,400,000,000
A2019 Capital Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Authorized amount of shares to repurchase   $ 3,940,000,000