Segment information (Details 9) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Segment Reporting Information
External sales and revenues	$ 14,342	$ 13,510	$ 14,011	$ 12,859	$ 12,896	$ 11,413	$ 11,331	$ 9,822	$ 54,722	$ 45,462	$ 38,537
Property, plant and equipment - net	13,574				14,155				13,574	14,155		$ 13,965
U.S. pensions
Segment Reporting Information
External sales and revenues									22,690	18,552	15,956
Property, plant and equipment - net	8,152				8,126				8,152	8,126
Outside the United States
Segment Reporting Information
External sales and revenues									32,032	26,910	$ 22,581
Property, plant and equipment - net	$ 5,422				$ 6,029				$ 5,422	$ 6,029