Income taxes Income taxes (Details 2) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency
Pre-tax foreign currency permanent difference				$ 180	$ (160)	$ 130
Taxes at U. S. statutory rate (as a percent)				21.00%	35.00%	35.00%
Adjustment to estimated tax for mandatory deemed repatriation of non-U.S. earnings	$ 50			$ 50
Adjustment to U.S. 2017 tax reform estimated impact				(104)
Correction of Prior Year Valuation Allowance		$ 59		59	$ (17)	$ (33)
U.S. 2017 tax reform provisionally estimated impact			$ 2,371		2,371
Charge/ (benefit) to U.S. deferred tax rate change 2017 U.S. tax reform		$ 154		(154)
Undistributed earnings of foreign subsidiaries	$ 14,000			14,000
Valuation allowances				(29)	(111)	141
U.S. state taxing jurisdictions
Income Tax Contingency
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount				(63)
Valuation allowances					$ (111)	$ 141
Outside the United States
Income Tax Contingency
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount				(25)
Discretionary Contribution
Income Tax Contingency
Payment for Pension and Other Postretirement Benefits				$ 1,000