Shareholders' equity Schedule of Dividends Declared (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares	Dec. 31, 2018 SFr / shares	Dec. 31, 2017 $ / shares	Dec. 31, 2017 SFr / shares	Dec. 31, 2016 $ / shares	Dec. 31, 2016 SFr / shares
Switzerland, Francs
Dividends Declared [Line Items]
Total dividend distributions per common share | SFr / shares		SFr 2.84		SFr 2.76		SFr 2.70
United States of America, Dollars
Dividends Declared [Line Items]
Total dividend distributions per common share | $ / shares	$ 2.90		$ 2.82		$ 2.74