Stockholders' equity - Components of accumulated other comprehensive income (loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period		$ 761	$ 761
Reclassification of currency translation adjustment to gain on disposal of discontinued	$ (64)		(64)
Balance at the end of period	901		901
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period	(4)	59	59
Other comprehensive (loss) income	1	(63)
Tax expense	(1)
Reclassification of currency translation adjustment to gain on disposal of discontinued	(64)
Balance at the end of period	(68)	(4)	(68)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period	77	126	126
Other comprehensive (loss) income		(49)
Reclassification of currency translation adjustment to gain on disposal of discontinued	(78)
Balance at the end of period	(1)	77	(1)
Unrecognized (Loss) Gain on Derivative Instruments
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period	(27)	(12)	(12)
Other comprehensive (loss) income	1	(15)
Tax expense	(1)
Reclassification of currency translation adjustment to gain on disposal of discontinued	(5)
Balance at the end of period	(32)	(27)	(32)
Pension Adjustments
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of period	(54)	(55)	(55)
Other comprehensive (loss) income		1
Reclassification of currency translation adjustment to gain on disposal of discontinued	19
Balance at the end of period	$ (35)	$ (54)	$ (35)