Shareholders' equity Dividends Declared (Details)	3 Months Ended
	Mar. 31, 2019 $ / shares	Mar. 31, 2019 SFr / shares	Mar. 31, 2018 $ / shares	Mar. 31, 2018 SFr / shares	May 31, 2018 $ / shares	May 31, 2017 $ / shares
Equity, Class of Treasury Stock [Line Items]
Annual dividend per share approved by shareholders					$ 2.92	$ 2.84
Common Stock, Dividend Rate Approved					$ 0.73	$ 0.71
United States of America, Dollars
Equity, Class of Treasury Stock [Line Items]
Common Stock, Dividends, Per Share, Declared	$ 0.73		$ 0.71
Switzerland, Francs
Equity, Class of Treasury Stock [Line Items]
Common Stock, Dividends, Per Share, Declared | SFr / shares		SFr 0.72		SFr 0.66