Postemployment benefit plans (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
U.S. Pension Benefits
Change in plan assets:
Fair value of plan assets, beginning of year	$ 11,440	$ 12,530
Actual return on plan assets	860	(225)
Foreign currency exchange rates	0	0
Company contributions	36	30
Participant contributions	0	0
Benefits paid	(970)	(890)
Settlements and termination benefits	(12)	(5)
Fair value of plan assets, end of year	$ 11,354	11,440
Information about plan asset allocations
Rebalancing of plan assets outside of target allocation (as a percent)	5.00%
U.S. Pension Benefits | Equities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	40.00%
U.S. Pension Benefits | Debt securities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	60.00%
U.S. Pension Benefits | Real estate
Change in plan assets:
Fair value of plan assets, beginning of year	$ 9
Fair value of plan assets, end of year	10	9
Non-U.S. Pension Benefits
Change in plan assets:
Fair value of plan assets, beginning of year	3,890	4,100
Actual return on plan assets	503	107
Foreign currency exchange rates	(392)	(234)
Company contributions	117	156
Participant contributions	7	8
Benefits paid	(238)	(191)
Settlements and termination benefits	0	(56)
Fair value of plan assets, end of year	$ 3,887	3,890
Non-U.S. Pension Benefits | Equities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	39.00%
Non-U.S. Pension Benefits | Debt securities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	52.00%
Non-U.S. Pension Benefits | Real estate
Change in plan assets:
Fair value of plan assets, beginning of year	$ 172
Fair value of plan assets, end of year	$ 179	172
Information about plan asset allocations
Target allocation of plan assets (as a percent)	6.00%
Non-U.S. Pension Benefits | Other
Information about plan asset allocations
Target allocation of plan assets (as a percent)	3.00%
Other Postretirement Benefits
Change in plan assets:
Fair value of plan assets, beginning of year	$ 650	776
Actual return on plan assets	55	3
Foreign currency exchange rates	0	0
Company contributions	176	164
Participant contributions	57	52
Benefits paid	(388)	(345)
Settlements and termination benefits	0	0
Fair value of plan assets, end of year	$ 550	$ 650
Other Postretirement Benefits | Equities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	70.00%
Other Postretirement Benefits | Debt securities
Information about plan asset allocations
Target allocation of plan assets (as a percent)	30.00%