Postretirement benefits Components of net periodic benefit costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Plan [Member] | UNITED STATES
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 14	$ 16
Interest cost	26	26
Expected return on plan assets	(53)	(47)
Amortization of prior service cost	0	0
Net periodic (benefit) cost	(13)	(5)
Pension Plan [Member] | Non-US [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	3	4
Interest cost	7	7
Expected return on plan assets	(13)	(10)
Amortization of prior service cost	0	0
Net periodic (benefit) cost	(3)	1
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0
Interest cost	1	1
Expected return on plan assets	(1)	(1)
Amortization of prior service cost	(21)	(23)
Net periodic (benefit) cost	$ (21)	$ (23)