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Shareholders' equity (Details) |  | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Aug. 04, 2021 shares | Sep. 30, 2021 SFr / shares shares | May 20, 2021 $ / shares | Dec. 31, 2020 SFr / shares shares | May 20, 2020 $ / shares | May 31, 2019 $ / shares
Stockholders' Equity Note [Abstract] |  |  |  |  |  |
Common Shares, par value | SFr / shares |  | SFr 24.15 |  | SFr 24.15 |  |
Common Shares in treasury, shares |  | 43,144,862 |  | 26,872,639 |  |
Treasury Stock, Shares, Retired | 3,584,150 |  |  |  |  |
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures |  | 3,021,027 |  |  |  |
Common Stock, Dividend Rate Approved | $ / shares |  |  | $ 0.80 |  | $ 0.78 | $ 0.75
Annual dividend per share approved by shareholders | $ / shares |  |  | $ 3.20 |  | $ 3.12 | $ 3.00
Nov 2020 Stock Repurchase Plan |  |  |  |  |  |
Stockholders' Equity Note [Abstract] |  |  |  |  |  |
Number of shares repurchased |  | 22,877,400 |  |  |  |

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