Postemployment benefit plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure
Change in service and interest cost from change in accounting estimate	$ (180)
Voluntary retirement enhancement program
Defined Benefit Plan Disclosure
Curtailment expense		$ (82)
U.S. Pension Benefits
Defined Benefit Plan Disclosure
Discount rate (as a percent)	4.50%	3.80%	4.60%
Change in service and interest cost from change in accounting estimate	$ 0	$ (1)	$ (17)
Non-U.S. Pension Benefits
Defined Benefit Plan Disclosure
Discount rate (as a percent)	2.90%	3.30%	4.10%
Change in service and interest cost from change in accounting estimate	$ (6)	$ (8)	$ (4)
Other Postretirement Benefits
Defined Benefit Plan Disclosure
Discount rate (as a percent)	4.20%	3.90%	4.60%
Change in service and interest cost from change in accounting estimate	$ (125)	$ 70	$ 53
Previous Accounting Method [Member] | U.S. Pension Benefits
Defined Benefit Plan Disclosure
Discount rate (as a percent)	4.20%
Previous Accounting Method [Member] | Non-U.S. Pension Benefits
Defined Benefit Plan Disclosure
Discount rate (as a percent)	3.20%
Previous Accounting Method [Member] | Other Postretirement Benefits
Defined Benefit Plan Disclosure
Discount rate (as a percent)	4.10%