Postretirement benefit plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
U.S. Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6	$ 6	$ 20	$ 18
Interest cost	12	11	33	33
Expected return on plan assets	(11)	(12)	(36)	(37)
Amortization of prior service cost (credit)	0	0	0	1
Recognized net actuarial loss	5	4	16	12
Net periodic benefit cost	12	9	33	27
Settlement loss	5	0	18	0
Curtailment gain	0	0	0	0
Special termination benefit gain	0	0	0	(2)
Total, including other postretirement losses (gains)	17	9	51	25
U.S. Retiree Health Care [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	4	4
Interest cost	5	6	15	18
Expected return on plan assets	(6)	(6)	(18)	(18)
Amortization of prior service cost (credit)	1	1	3	3
Recognized net actuarial loss	3	4	9	10
Net periodic benefit cost	4	6	13	17
Settlement loss	0	0	0	0
Curtailment gain	0	0	0	(1)
Special termination benefit gain	0	0	0	0
Total, including other postretirement losses (gains)	4	6	13	16
Non-U.S. Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	10	29	29
Interest cost	15	19	46	58
Expected return on plan assets	(17)	(20)	(50)	(59)
Amortization of prior service cost (credit)	(1)	(1)	(3)	(3)
Recognized net actuarial loss	7	10	24	34
Net periodic benefit cost	13	18	46	59
Settlement loss	4	193	4	193
Curtailment gain	(2)	0	(5)	0
Special termination benefit gain	0	(337)	0	(337)
Total, including other postretirement losses (gains)	$ 15	$ (126)	$ 45	$ (85)