Postemployment benefit plans (Details 8) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other changes in plan assets and benefit obligations recognized in other comprehensive income (pre-tax):
Total recognized in other comprehensive income	$ (180)
U.S. Pension Benefits
Components of net periodic benefit cost:
Service cost	119	$ 181	$ 157
Interest cost	517	608	648
Expected return on plan assets	(757)	(890)	(943)
Defined benefit plan curtailment and settlement losses	6	32	0
Amortization of:
Prior service cost / (credit)	0	1	17
Net actuarial loss / (gain)	664	732	2,088
Total cost included in operating profit	549	664	1,967
Other changes in plan assets and benefit obligations recognized in other comprehensive income (pre-tax):
Current year prior service cost (credit)	0	0	0
Amortization of prior service (cost) credit	0	(1)	(17)
Total recognized in other comprehensive income	0	(1)	(17)
Total recognized in net periodic cost and other comprehensive income	$ 549	$ 663	$ 1,950
Weighted-average assumptions used to determine net cost:
Discount rate (as a percent)	4.50%	3.80%	4.60%
Discount rate used to measure interest cost	3.40%	3.80%	4.60%
Expected return on plan assets (as a percent)	6.90%	7.40%	7.80%
Rate of compensation increase (as a percent)	4.00%	4.00%	4.00%
Expected return on plan assets, next fiscal year (as a percent)	6.70%
Additional percentage amount added to long-term passive rate of returns to arrive at the long-term expected rate of return (as a percent)	0.90%	0.95%	1.00%
Non-U.S. Pension Benefits
Components of net periodic benefit cost:
Service cost	$ 92	$ 110	$ 109
Interest cost	117	146	185
Expected return on plan assets	(227)	(273)	(271)
Defined benefit plan curtailment and settlement losses	1	(1)	2
Amortization of:
Prior service cost / (credit)	3	0	0
Net actuarial loss / (gain)	262	8	345
Total cost included in operating profit	248	(10)	370
Other changes in plan assets and benefit obligations recognized in other comprehensive income (pre-tax):
Current year prior service cost (credit)	(3)	(8)	(4)
Amortization of prior service (cost) credit	(3)	0	0
Total recognized in other comprehensive income	(6)	(8)	(4)
Total recognized in net periodic cost and other comprehensive income	$ 242	$ (18)	$ 366
Weighted-average assumptions used to determine net cost:
Discount rate (as a percent)	2.90%	3.30%	4.10%
Discount rate used to measure interest cost	2.80%	3.30%	4.10%
Expected return on plan assets (as a percent)	6.10%	6.80%	6.90%
Rate of compensation increase (as a percent)	3.60%	4.00%	4.20%
Expected return on plan assets, next fiscal year (as a percent)	5.90%
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost	$ 82	$ 101	$ 82
Interest cost	131	181	213
Expected return on plan assets	(44)	(56)	(58)
Defined benefit plan curtailment and settlement losses	(9)	27	(4)
Amortization of:
Prior service cost / (credit)	(59)	(54)	(55)
Net actuarial loss / (gain)	59	(561)	191
Total cost included in operating profit	160	(362)	369
Other changes in plan assets and benefit obligations recognized in other comprehensive income (pre-tax):
Current year prior service cost (credit)	(184)	16	(2)
Amortization of prior service (cost) credit	59	54	55
Total recognized in other comprehensive income	(125)	70	53
Total recognized in net periodic cost and other comprehensive income	$ 35	$ (292)	$ 422
Weighted-average assumptions used to determine net cost:
Discount rate (as a percent)	4.20%	3.90%	4.60%
Discount rate used to measure interest cost	3.30%	3.90%	4.60%
Expected return on plan assets (as a percent)	7.50%	7.80%	7.80%
Rate of compensation increase (as a percent)	4.00%	4.00%	4.00%
Assumed increase in health care trend rate
Assumed increase in health care trend rate over the current period to calculate benefit expenses (as a percent)	6.50%
Assumed increase in health care trend rate for the next year to calculate benefit expenses (as a percent)	6.60%
Year that heath care trend rate is assumed to reach ultimate trend rate (year)	2022
Ultimate health care cost trend rate (as a percent)	5.00%
General inflation rate that forms a part of ultimate health care trend rate (as a percent)	3.00%
Additional healthcare inflation rate that forms a part of ultimate health care trend rate (as a percent)	2.00%