Postretirement benefit plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
U.S. Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5		$ 7		$ 10		$ 14
Interest cost	11		10		22		21
Expected return on plan assets	(11)		(12)		(21)		(25)
Amortization of prior service cost (credit)	0		0		0		0
Recognized net actuarial loss	7		5		13		11
Net periodic benefit costs	12		10		24		21
Settlement losses	2	[1]	6	[1]	3	[1]	13	[1]
Curtailment gain	0		0		0		0
Total, including other postretirement (gains) losses	14		16		27		34
U.S. Retiree Health Care
Defined Benefit Plan Disclosure [Line Items]
Service cost	1		2		2		3
Interest cost	6		5		11		10
Expected return on plan assets	(5)		(6)		(10)		(12)
Amortization of prior service cost (credit)	1		1		2		2
Recognized net actuarial loss	2		3		4		6
Net periodic benefit costs	5		5		9		9
Settlement losses	0	[1]	0	[1]	0	[1]	0	[1]
Curtailment gain	0		0		0		0
Total, including other postretirement (gains) losses	5		5		9		9
Non-U.S. Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	10		10		20		20
Interest cost	18		15		35		31
Expected return on plan assets	(22)		(16)		(41)		(33)
Amortization of prior service cost (credit)	0		(1)		(1)		(2)
Recognized net actuarial loss	7		7		13		17
Net periodic benefit costs	13		15		26		33
Settlement losses	0	[1]	0	[1]	0	[1]	0	[1]
Curtailment gain	0		(3)		0		(3)
Total, including other postretirement (gains) losses	$ 13		$ 12		$ 26		$ 30

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