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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6	$ 5	$ 11	$ 9
Interest cost	7	8	15	17
Expected return on plan assets	(9)	(9)	(17)	(18)
Recognized net actuarial loss	4	2	8	4
Net periodic benefit costs	8	6	17	12
Settlement losses	4	3	8	7
Total, including other postretirement losses	12	9	25	19
U.S. | Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	0	2	1
Interest cost	2	3	5	6
Expected return on plan assets	(3)	(3)	(6)	(6)
Recognized net actuarial loss	0	0	0	0
Net periodic benefit costs	0	0	1	1
Settlement losses	0	0	0	0
Total, including other postretirement losses	0	0	1	1
Non-U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	8	18	16
Interest cost	10	10	19	19
Expected return on plan assets	(21)	(20)	(41)	(38)
Recognized net actuarial loss	2	4	4	7
Net periodic benefit costs	0	2	0	4
Settlement losses	0	0	1	1
Total, including other postretirement losses	$ 0	$ 2	$ 1	$ 5