Shareholders' equity Schedule of Dividends Declared (Details)	12 Months Ended
	Dec. 31, 2016 $ / shares	Dec. 31, 2016 SFr / shares	Dec. 31, 2015 $ / shares	Dec. 31, 2015 SFr / shares	Dec. 31, 2014 $ / shares	Dec. 31, 2014 SFr / shares
Switzerland, Francs
Dividends Declared [Line Items]
Dividends - par value reduction | SFr / shares		SFr 0		SFr 0.62		SFr 2.27
Dividends - distributed from capital contribution reserves | SFr / shares		2.70		1.94		0.20
Total dividend distributions per common share | SFr / shares		SFr 2.70		SFr 2.56		SFr 2.47
United States of America, Dollars
Dividends Declared [Line Items]
Dividends - par value reduction | $ / shares	$ 0		$ 0.65		$ 2.46
Dividends - distributed from capital contribution reserves | $ / shares	2.74		2.01		0.24
Total dividend distributions per common share | $ / shares	$ 2.74		$ 2.66		$ 2.70