Employee benefit plans - Combined Data for Defined Benefit Pension and Post Retirement Healthcare Plans (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits | Domestic
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0	$ 0
Interest cost	39	39	44	117	133
Expected return on assets	(80)	(79)	(84)	(239)	(252)
Other	22	21	13	65	39
Net periodic benefit (credit) cost	(19)	(19)	(27)	(57)	(80)
Pension Benefits | Foreign
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	3	9	9
Interest cost	7	6	8	20	24
Expected return on assets	(10)	(9)	(11)	(29)	(34)
Other	2	3	0	8	1
Net periodic benefit (credit) cost	2	3	0	8	0
Healthcare Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0	0
Interest cost	2	1	2	4	5
Expected return on assets	(2)	(2)	(1)	(5)	(5)
Other	(1)	0	(1)	(2)	(2)
Net periodic benefit (credit) cost	$ (1)	$ (1)	$ 0	$ (3)	$ (2)