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