Shareholders' equity Dividends declared (Details)	3 Months Ended				6 Months Ended
	Jun. 30, 2017 $ / shares	Jun. 30, 2017 SFr / shares	Jun. 30, 2016 $ / shares	Jun. 30, 2016 SFr / shares	Jun. 30, 2017 $ / shares	Jun. 30, 2017 SFr / shares	Jun. 30, 2016 $ / shares	Jun. 30, 2016 SFr / shares
Dividends Declared [Abstract]
Common Stock, Dividend Rate Declared | (per share)	$ 0.71	SFr 0.69	$ 0.69	SFr 0.68	$ 1.40	SFr 1.38	$ 1.36	SFr 1.34