Stockholders' equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common Stock
Stockholders' equity
Reclassification of APIC due to U.S. Domestication	$ (1,713)
Additional paid in capital
Stockholders' equity
Reclassification of APIC due to U.S. Domestication	$ 1,713