Stockholders' equity (Details Textual) (Details) - USD ($)	1 Months Ended			3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Class of Stock [Line Items]
Stock repurchase program, additional authorized amount			$ 4,000,000,000.0
Amount available for stock repurchases under a board approved stock repurchase plan		$ 5,500,000,000		$ 5,500,000,000
Dividends declared per share (in usd per share)		$ 1.60	$ 1.60	$ 1.60	$ 1.45
Dividends paid per share (in usd per share)		$ 1.60
Forecast [Member]
Class of Stock [Line Items]
Dividends paid per share (in usd per share)	$ 1.60