Postretirement benefit plans - Expense Related to Defined Benefit and Retiree Health Care Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 5	$ 9	$ 9
Interest cost	8	10	17	19
Expected return on plan assets	(9)	(12)	(18)	(21)
Recognized net actuarial loss	2	3	4	5
Net periodic benefit costs	6	6	12	12
Settlement losses	3	3	7	6
Total, including other postretirement losses	9	9	19	18
U.S. | Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1	1
Interest cost	3	4	6	7
Expected return on plan assets	(3)	(3)	(6)	(7)
Recognized net actuarial loss	0	0	0	0
Net periodic benefit costs	0	1	1	1
Settlement losses	0	0	0	0
Total, including other postretirement losses	0	1	1	1
Non-U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	8	16	16
Interest cost	10	11	19	22
Expected return on plan assets	(20)	(23)	(38)	(44)
Recognized net actuarial loss	4	8	7	15
Net periodic benefit costs	2	4	4	9
Settlement losses	0	1	1	2
Total, including other postretirement losses	$ 2	$ 5	$ 5	$ 11