Supplemental financial information - Property, plant and equipment at cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	$ 5,465	$ 6,266
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	127	137
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	$ 2,789	2,801
Buildings and improvements | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost, depreciable lives	5 years
Buildings and improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost, depreciable lives	40 years
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	$ 2,549	$ 3,328
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost, depreciable lives	3 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost, depreciable lives	10 years