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Stock-based compensation (Components of Stock-based Compensation Expense) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Components of stock-based compensation expense [Abstract]      
Total stock-based compensation expense, pretax $ 308 $ 311 $ 329
Tax benefit from stock-based compensation expense (67) (67) (118)
Total stock-based compensation expense, net of tax 241 244 211
RSUs [Member]      
Components of stock-based compensation expense [Abstract]      
Total stock-based compensation expense, pretax 168 165 174
Performance units [Member]      
Components of stock-based compensation expense [Abstract]      
Total stock-based compensation expense, pretax 105 117 133
Stock options [Member]      
Components of stock-based compensation expense [Abstract]      
Total stock-based compensation expense, pretax $ 35 $ 29 $ 22