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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 4	$ 14	$ 13
Interest cost	7	9	24	28
Expected return on plan assets	(9)	(10)	(27)	(31)
Recognized net actuarial loss	1	3	5	8
Amortization of prior service cost (credit)	0	0	0	0
Net periodic benefit costs	4	6	16	18
Settlement losses	3	3	10	9
Total, including other postretirement losses	7	9	26	27
U.S. | Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	2	2
Interest cost	3	4	9	11
Expected return on plan assets	(2)	(4)	(8)	(11)
Recognized net actuarial loss	0	0	0	0
Amortization of prior service cost (credit)	(1)	(1)	(1)	(1)
Net periodic benefit costs	1	0	2	1
Settlement losses	0	0	0	0
Total, including other postretirement losses	1	0	2	1
Non-U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	7	25	23
Interest cost	9	11	28	33
Expected return on plan assets	(20)	(20)	(58)	(64)
Recognized net actuarial loss	4	6	11	21
Amortization of prior service cost (credit)	0	1	0	1
Net periodic benefit costs	2	5	6	14
Settlement losses	1	0	2	2
Total, including other postretirement losses	$ 3	$ 5	$ 8	$ 16