Postretirement benefit plans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
U.S. Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6	$ 6
Interest cost	11	11
Expected return on plan assets	(12)	(11)
Amortization of prior service cost (credit)	0	0
Recognized net actuarial loss	4	6
Net periodic benefit cost	9	12
Curtailment charges (credits)	0	0
Special termination benefit charges (credits)	(2)	0
Total, including charges	7	12
U.S. Retiree Health Care [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1
Interest cost	6	6
Expected return on plan assets	(5)	(5)
Amortization of prior service cost (credit)	1	1
Recognized net actuarial loss	3	3
Net periodic benefit cost	6	6
Curtailment charges (credits)	(1)	0
Special termination benefit charges (credits)	0	0
Total, including charges	5	6
Non-U.S. Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	9
Interest cost	19	16
Expected return on plan assets	(20)	(19)
Amortization of prior service cost (credit)	(1)	(1)
Recognized net actuarial loss	12	9
Net periodic benefit cost	20	14
Curtailment charges (credits)	0	0
Special termination benefit charges (credits)	0	0
Total, including charges	$ 20	$ 14