Shareholders' equity (Details)			3 Months Ended
	Mar. 07, 2025 shares	May 21, 2024 shares	Mar. 31, 2026 SFr / shares shares	Dec. 31, 2025 SFr / shares shares	May 16, 2024 $ / shares	May 17, 2023 $ / shares
Stockholders' Equity Note [Abstract]
Common Shares, par value | SFr / shares			SFr 0.50	SFr 0.50
Annual dividend per share approved by shareholders | $ / shares					$ 3.88	$ 3.64
Common Stock, Dividend Rate Approved | $ / shares					0.97	0.91
Treasury Stock, Shares, Retired | shares	11,986,574	7,518,565	11,986,574
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures | shares			912,163
Equity, Class of Treasury Stock [Line Items]
Common Stock, Dividend Rate Approved | $ / shares					0.97	0.91
Treasury Stock, Shares, Retired | shares	11,986,574	7,518,565	11,986,574
Treasury Stock, Common, Shares | shares			11,625,267	21,006,194
Common Shares, par value | SFr / shares			SFr 0.50	SFr 0.50
Annual dividend per share approved by shareholders | $ / shares					$ 3.88	$ 3.64