Segment information (Details 8) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information
External sales and revenues	$ 12,896	$ 11,413	$ 11,331	$ 9,822	$ 9,574	$ 9,160	$ 10,342	$ 9,461	$ 45,462	$ 38,537	$ 47,011
Net property, plant and equipment	14,155				15,322				14,155	15,322
U.S. Pension Benefits
Segment Reporting Information
External sales and revenues									18,552	15,956	19,218
Net property, plant and equipment	8,126				8,537				8,126	8,537
Outside the United States
Segment Reporting Information
External sales and revenues									26,910	22,581	$ 27,793
Net property, plant and equipment	$ 6,029				$ 6,785				$ 6,029	$ 6,785