Shareholders' equity (Details)		3 Months Ended
	Jan. 17, 2022 shares	Mar. 31, 2022 SFr / shares shares	Mar. 31, 2021 shares	Dec. 31, 2021 SFr / shares shares	May 20, 2021 $ / shares	May 20, 2020 $ / shares
Stockholders' Equity Note [Abstract]
Common Shares, par value | SFr / shares		SFr 24.15		SFr 24.15
Common Shares in treasury, shares		35,880,387		47,448,502
Treasury Stock, Shares, Retired	14,465,400
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures		1,972,615
Common Stock, Dividend Rate Approved | $ / shares					$ 0.80	$ 0.78
Annual dividend per share approved by shareholders | $ / shares					$ 3.20	$ 3.12
Nov 2020 Stock Repurchase Plan
Stockholders' Equity Note [Abstract]
Number of shares repurchased			3,110,000