Postretirement benefit plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Settlement losses					$ 15		$ 22
U.S. Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	6		6		16		20
Interest cost	11		12		33		33
Expected return on plan assets	(10)		(11)		(31)		(36)
Amortization of prior service cost (credit)	0		0		0		0
Recognized net actuarial loss	6		5		19		16
Net periodic benefit costs	13		12		37		33
Settlement losses	11	[1]	5	[1]	14	[1]	18	[1]
Curtailment gain	0		0		0		0
Total, including other postretirement (gains) losses	24		17		51		51
U.S. Retiree Health Care
Defined Benefit Plan Disclosure [Line Items]
Service cost	1		1		3		4
Interest cost	6		5		17		15
Expected return on plan assets	(5)		(6)		(15)		(18)
Amortization of prior service cost (credit)	1		1		3		3
Recognized net actuarial loss	1		3		5		9
Net periodic benefit costs	4		4		13		13
Settlement losses	0	[1]	0	[1]	0	[1]	0	[1]
Curtailment gain	0		0		0		0
Total, including other postretirement (gains) losses	4		4		13		13
Non-U.S. Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	9		9		29		29
Interest cost	17		15		52		46
Expected return on plan assets	(21)		(17)		(62)		(50)
Amortization of prior service cost (credit)	0		(1)		(1)		(3)
Recognized net actuarial loss	6		7		19		24
Net periodic benefit costs	11		13		37		46
Settlement losses	1	[1]	4	[1]	1	[1]	4	[1]
Curtailment gain	(2)		(2)		(2)		(5)
Total, including other postretirement (gains) losses	$ 10		$ 15		$ 36		$ 45

[1] Includes non-restructuring and restructuring-related settlement losses.