Stockholders' equity (Components of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	$ 10,659	$ 9,485	$ 9,673	$ 10,794	$ 9,673	$ 12,500
Foreign currency translation adjustments	14			(39)	(41)	(56)
Balance as of end of period	10,959	10,659	9,485	10,927	10,959	10,927
Foreign currency translation [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	(773)	(770)	(718)		(718)
Foreign currency translation adjustments	14	(3)	(52)
Income taxes	0	0	0
Balance as of end of period	(759)	(773)	(770)		(759)
Cash flow hedges [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	(2)	114	175		175
Unrealized (losses) gains	60	(30)	(162)
Reclassification adjustments to income	(224)	(119)	84
Income taxes	(36)	(33)	(17)
Balance as of end of period	(130)	(2)	114		(130)
Available-for-sale securities [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	1	3	22		22
Unrealized (losses) gains	1	(2)	8
Reclassification adjustments to income	0	0	(33)
Income taxes	0	0	(6)
Balance as of end of period	2	1	3		2
Other [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	(9)	(9)	(7)		(7)
Unrealized (losses) gains	0	0	0
Other	(7)	0	(2)
Balance as of end of period	(16)	(9)	(9)		(16)
AOCI [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	(783)	(662)	(528)	(465)	(528)	(769)
Foreign currency translation adjustments	14	(3)	(52)
Unrealized (losses) gains	61	(32)	(154)
Reclassification adjustments to income	(224)	(119)	51
Other	(7)	0	(2)
Income taxes	36	33	23
Balance as of end of period	$ (903)	$ (783)	$ (662)	$ (388)	$ (903)	$ (388)