Postemployment benefit plans (Details 2) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Actuarial losses (gains)	$ 468	$ 495	$ 468	$ 495	$ 301
Components of net amount recognized in financial position:
Liability for postemployment benefits	$ 6,599	$ 7,455	$ 6,599	$ 7,455
U.S. pensions
Weighted-average assumptions used to determine benefit obligation, end of year:
Discount rate (as a percent)	3.20%	4.20%	3.20%	4.20%
Rate of compensation increase (as a percent)	0.00%	4.00%	0.00%	4.00%
Accumulated benefit obligation, end of year	$ 17,773	$ 15,877	$ 17,773	$ 15,877
Change in benefit obligation:
Benefit obligation, beginning of year			15,953	17,326
Service cost			115	125	115
Interest cost			600	534	525
Plan amendments			0	0
Actuarial losses (gains)			2,090	(1,058)
Foreign currency exchange rates			0	0
Participant contributions			0	0
Benefits paid - gross			(982)	(971)
Less: federal subsidy on benefits paid			0	0
Curtailments, settlements and termination benefits			(3)	(3)
Benefit obligation, end of year	17,773	15,953	17,773	15,953	17,326
Change in plan assets:
Fair value of plan assets, beginning of year			12,697	13,416
Actual return on plan assets			2,740	(784)
Foreign currency exchange rates			0	0
Company contributions			1,542	1,039
Participant contributions			0	0
Benefits paid			(982)	(971)
Settlements and termination benefits			(3)	(3)
Fair value of plan assets, end of year	15,994	12,697	15,994	12,697	13,416
Funded Status, end of year
Over (under) funded status	(1,779)	(3,256)	(1,779)	(3,256)
Components of net amount recognized in financial position:
Other assets (non-current asset)	219	9	219	9
Accrued wages, salaries and employee benefits (current liability)	(42)	(40)	(42)	(40)
Liability for postemployment benefits (non-current liability)	(1,956)	(3,225)	(1,956)	(3,225)
Net liability recognized	(1,779)	(3,256)	(1,779)	(3,256)
Amounts recognized in Accumulated other comprehensive income (pre-tax) consist of:
Prior service cost (credit)	$ 0	$ 0	$ 0	$ 0
Non-U.S. pensions
Weighted-average assumptions used to determine benefit obligation, end of year:
Discount rate (as a percent)	1.90%	2.50%	1.90%	2.50%
Rate of compensation increase (as a percent)	2.00%	3.00%	2.00%	3.00%
Accumulated benefit obligation, end of year	$ 4,502	$ 4,038	$ 4,502	$ 4,038
Change in benefit obligation:
Benefit obligation, beginning of year			4,215	4,606
Service cost			80	89	95
Interest cost			94	96	101
Plan amendments			(5)	26
Actuarial losses (gains)			424	(88)
Foreign currency exchange rates			95	(205)
Participant contributions			7	6
Benefits paid - gross			(237)	(277)
Less: federal subsidy on benefits paid			0	0
Curtailments, settlements and termination benefits			(7)	(38)
Benefit obligation, end of year	4,666	4,215	4,666	4,215	4,606
Change in plan assets:
Fair value of plan assets, beginning of year			4,025	4,305
Actual return on plan assets			482	13
Foreign currency exchange rates			105	(187)
Company contributions			143	165
Participant contributions			7	6
Benefits paid			(237)	(277)
Settlements and termination benefits			0	0
Fair value of plan assets, end of year	4,525	4,025	4,525	4,025	4,305
Funded Status, end of year
Over (under) funded status	(141)	(190)	(141)	(190)
Components of net amount recognized in financial position:
Other assets (non-current asset)	485	442	485	442
Accrued wages, salaries and employee benefits (current liability)	(19)	(20)	(19)	(20)
Liability for postemployment benefits (non-current liability)	(607)	(612)	(607)	(612)
Net liability recognized	(141)	(190)	(141)	(190)
Amounts recognized in Accumulated other comprehensive income (pre-tax) consist of:
Prior service cost (credit)	$ 16	$ 20	$ 16	$ 20
Other postretirement benefits
Weighted-average assumptions used to determine benefit obligation, end of year:
Discount rate (as a percent)	3.20%	4.20%	3.20%	4.20%
Rate of compensation increase (as a percent)	4.00%	4.00%	4.00%	4.00%
Change in benefit obligation:
Benefit obligation, beginning of year			$ 3,649	$ 4,002
Service cost			80	83	78
Interest cost			136	125	130
Plan amendments			8	(25)
Actuarial losses (gains)			350	(195)
Foreign currency exchange rates			(1)	(28)
Participant contributions			46	51
Benefits paid - gross			(316)	(369)
Less: federal subsidy on benefits paid			9	7
Curtailments, settlements and termination benefits			(1)	(2)
Benefit obligation, end of year	$ 3,960	$ 3,649	3,960	3,649	4,002
Change in plan assets:
Fair value of plan assets, beginning of year			328	504
Actual return on plan assets			71	(5)
Foreign currency exchange rates			0	0
Company contributions			127	147
Participant contributions			46	51
Benefits paid			(316)	(369)
Settlements and termination benefits			(1)	0
Fair value of plan assets, end of year	255	328	255	328	$ 504
Funded Status, end of year
Over (under) funded status	(3,705)	(3,321)	(3,705)	(3,321)
Components of net amount recognized in financial position:
Other assets (non-current asset)	0	0	0	0
Accrued wages, salaries and employee benefits (current liability)	(161)	(173)	(161)	(173)
Liability for postemployment benefits (non-current liability)	(3,544)	(3,148)	(3,544)	(3,148)
Net liability recognized	(3,705)	(3,321)	(3,705)	(3,321)
Liability for postemployment benefits	60	119	60	119
Amounts recognized in Accumulated other comprehensive income (pre-tax) consist of:
Prior service cost (credit)	(78)	(126)	(78)	(126)
Defined contribution
Components of net amount recognized in financial position:
Liability for postemployment benefits	$ 432	$ 351	$ 432	$ 351