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 |