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Shareholders' equity Share Repurchases (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | ---
Oct. 30, 2019 | Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 01, 2018 | Dec. 21, 2017
2019 Stock Repurchase Plan [Member] |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |
Stock Repurchase Program, Authorized Amount |  |  |  |  |  | $ 1,500 |
Number of shares repurchased |  | 3,079,618 |  | 8,417,838 |  |  |
Cost of shares repurchased |  | $ 478 |  | $ 1,221 |  |  |
Repurchase authorization remaining at end of period |  | $ 258 |  | $ 258 |  |  |
2018 Stock Repurchase Plan [Member] |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |
Stock Repurchase Program, Authorized Amount |  |  |  |  |  |  | $ 1,000
Number of shares repurchased |  |  | 2,781,307 |  | 5,225,162 |  |
Cost of shares repurchased |  |  | $ 379 |  | $ 703 |  |
Repurchase authorization remaining at end of period |  |  | $ 297 |  | $ 297 |  |
Subsequent Event [Member] | 2019 Stock Repurchase Plan [Member] |  |  |  |  |  |  |
Equity, Class of Treasury Stock [Line Items] |  |  |  |  |  |  |
Number of shares repurchased | 700,900 |  |  |  |  |  |
Cost of shares repurchased | $ 108 |  |  |  |  |  |
Repurchase authorization remaining at end of period | $ 150 |  |  |  |  |  |

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