Stockholders' equity - Components of accumulated other comprehensive income (loss) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period	$ 761
Balance at the end of period	656
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period	59
Other comprehensive income (loss)	(63)
Balance at the end of period	(4)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period	126
Other comprehensive income (loss)	(49)
Balance at the end of period	77
Unrecognized (Loss) Gain on Derivative Instruments
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period	(12)
Other comprehensive income (loss)	(15)
Balance at the end of period	(27)
Pension Adjustments
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period	(55)
Other comprehensive income (loss)	1
Balance at the end of period	$ (54)