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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4	$ 5	$ 13	$ 15
Interest cost	9	9	28	27
Expected return on plan assets	(10)	(11)	(31)	(32)
Recognized net actuarial loss	3	4	8	12
Amortization of prior service cost (credit)	0	0	0	0
Net periodic benefit costs	6	7	18	22
Settlement losses	3	9	9	11
Total, including other postretirement losses	9	16	27	33
U.S. | Retiree health care plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	2	3
Interest cost	4	4	11	11
Expected return on plan assets	(4)	(4)	(11)	(11)
Recognized net actuarial loss	0	1	0	2
Amortization of prior service cost (credit)	(1)	(1)	(1)	(2)
Net periodic benefit costs	0	1	1	3
Settlement losses	0	0	0	0
Total, including other postretirement losses	0	1	1	3
Non-U.S. | Defined benefit plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	8	23	26
Interest cost	11	11	33	34
Expected return on plan assets	(20)	(16)	(64)	(50)
Recognized net actuarial loss	6	5	21	16
Amortization of prior service cost (credit)	1	0	1	(1)
Net periodic benefit costs	5	8	14	25
Settlement losses	0	1	2	2
Total, including other postretirement losses	$ 5	$ 9	$ 16	$ 27