Postretirement benefit plans - Expense Related to Defined Benefit and Retiree Health Care Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	$ 4
Interest cost	9	9
Expected return on plan assets	(9)	(9)
Recognized net actuarial loss	2	2
Net periodic benefit costs	6	6
Settlement losses	4	3
Total, including other postretirement losses	10	9
U.S. | Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	3	3
Expected return on plan assets	(3)	(4)
Recognized net actuarial loss	0	0
Net periodic benefit costs	1	0
Settlement losses	0	0
Total, including other postretirement losses	1	0
Non-U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	8	8
Interest cost	9	11
Expected return on plan assets	(18)	(21)
Recognized net actuarial loss	3	7
Net periodic benefit costs	2	5
Settlement losses	1	1
Total, including other postretirement losses	$ 3	$ 6