Employee benefit plans - Combined Data for Defined Benefit Pension and Post Retirement Healthcare Plans (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits | Domestic
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0	$ 0
Interest cost	39	39	45	78	89
Expected return on assets	(79)	(80)	(84)	(159)	(168)
Other	21	22	13	43	26
Net periodic benefit (credit) cost	(19)	(19)	(26)	(38)	(53)
Pension Benefits | Foreign
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	3	3	6	6
Interest cost	6	7	8	13	16
Expected return on assets	(9)	(10)	(12)	(19)	(23)
Other	3	3	1	6	1
Net periodic benefit (credit) cost	3	3	0	6	0
Healthcare Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0	0
Interest cost	1	1	1	2	3
Expected return on assets	(2)	(1)	(2)	(3)	(4)
Other	0	(1)	0	(1)	(1)
Net periodic benefit (credit) cost	$ (1)	$ (1)	$ (1)	$ (2)	$ (2)