Postemployment benefit plans (Details 6) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
U.S. Pension Benefits
Funded Status, end of year
Fair value of plan assets, end of year	$ 11,354	$ 11,440	$ 12,530
Benefit obligations, end of year	16,218	15,792	16,249
Over (under) funded status recognized in financial position	(4,864)	(4,352)
Components of net amount recognized in financial position:
Other assets (non-current asset)	4	6
Accrued wages, salaries and employee benefits (current liability)	(35)	(32)
Liability for postemployment benefits (non-current liability)	(4,833)	(4,326)
Net liability recognized	(4,864)	(4,352)
Amounts recognized in Accumulated other comprehensive income (pre-tax) consist of:
Prior service cost (credit)	0	1
Estimated amounts that will be amortized from Accumulated other comprehensive income (loss) during the next fiscal year
Prior service cost (credit)	0
Pension plans with projected benefit obligations in excess of plan assets
Projected benefit obligation	16,163	15,734
Accumulated benefit obligation	15,979	15,493
Fair value of plan assets	11,295	11,377
Pension plans with accumulated benefit obligations in excess of plan assets
Projected benefit obligation	16,163	15,734
Accumulated benefit obligation	15,979	15,493
Fair value of plan assets	11,295	11,377
Non-U.S. Pension Benefits
Funded Status, end of year
Fair value of plan assets, end of year	3,887	3,890	4,100
Benefit obligations, end of year	4,472	4,355	4,801
Over (under) funded status recognized in financial position	(585)	(465)
Components of net amount recognized in financial position:
Other assets (non-current asset)	152	163
Accrued wages, salaries and employee benefits (current liability)	(20)	(19)
Liability for postemployment benefits (non-current liability)	(717)	(609)
Net liability recognized	(585)	(465)
Amounts recognized in Accumulated other comprehensive income (pre-tax) consist of:
Prior service cost (credit)	(5)	1
Estimated amounts that will be amortized from Accumulated other comprehensive income (loss) during the next fiscal year
Prior service cost (credit)	(1)
Pension plans with projected benefit obligations in excess of plan assets
Projected benefit obligation	4,098	1,818
Accumulated benefit obligation	3,835	1,657
Fair value of plan assets	3,361	1,190
Pension plans with accumulated benefit obligations in excess of plan assets
Projected benefit obligation	1,707	1,363
Accumulated benefit obligation	1,607	1,320
Fair value of plan assets	1,024	793
Other Postretirement Benefits
Funded Status, end of year
Fair value of plan assets, end of year	550	650	776
Benefit obligations, end of year	4,088	4,313	$ 4,938
Over (under) funded status recognized in financial position	(3,538)	(3,663)
Components of net amount recognized in financial position:
Other assets (non-current asset)	0	0
Accrued wages, salaries and employee benefits (current liability)	(162)	(161)
Liability for postemployment benefits (non-current liability)	(3,376)	(3,502)
Net liability recognized	(3,538)	(3,663)
Amounts recognized in Accumulated other comprehensive income (pre-tax) consist of:
Prior service cost (credit)	(85)	$ 39
Estimated amounts that will be amortized from Accumulated other comprehensive income (loss) during the next fiscal year
Prior service cost (credit)	$ (21)