Postretirement benefit plans - Expense Related to Defined Benefit and Retiree Health Care Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 5	$ 16	$ 14
Interest cost	8	7	23	24
Expected return on plan assets	(8)	(9)	(25)	(27)
Recognized net actuarial loss	3	1	11	5
Amortization of prior service cost (credit)	0	0	0	0
Net periodic benefit costs	8	4	25	16
Settlement losses	4	3	12	10
Total, including other postretirement losses	12	7	37	26
U.S. | Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	2	2
Interest cost	3	3	8	9
Expected return on plan assets	(2)	(2)	(8)	(8)
Recognized net actuarial loss	0	0	0	0
Amortization of prior service cost (credit)	(1)	(1)	(1)	(1)
Net periodic benefit costs	0	1	1	2
Settlement losses	0	0	0	0
Total, including other postretirement losses	0	1	1	2
Non-U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	9	27	25
Interest cost	9	9	28	28
Expected return on plan assets	(20)	(20)	(61)	(58)
Recognized net actuarial loss	2	4	6	11
Amortization of prior service cost (credit)	0	0	0	0
Net periodic benefit costs	0	2	0	6
Settlement losses	1	1	2	2
Total, including other postretirement losses	$ 1	$ 3	$ 2	$ 8