Income taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
(Decreases) increases in taxes resulting from:
Taxes at U.S. statutory rate	$ 1,643	$ 1,429	$ 49
Taxes at U. S. statutory rate (as a percent)	21.00%	35.00%	35.00%
Non-U.S. subsidiaries taxed at other than the U.S. rate	$ 282	$ (282)	$ (119)
Non-U.S. subsidiaries taxed at other than the U.S. rate (as a percent)	3.60%	(6.90%)	(85.60%)
State and local taxes, net of federal	$ 22	$ 27	$ (1)
State and local taxes, net of federal (as a percent)	0.30%	0.70%	(0.70%)
Interest and penalties, net of tax	$ 33	$ 28	$ 24
Interest and penalties, net of tax (as a percent)	0.40%	0.70%	17.20%
U.S. tax incentives	$ (106)	$ (52)	$ (52)
U.S. tax incentives (as a percent)	(1.30%)	(1.30%)	(37.40%)
ESOP dividend tax benefit	$ (12)	$ (21)	$ (27)
ESOP dividend tax benefit (as a percent)	(0.20%)	(0.50%)	(19.40%)
Net excess tax benefits from stock-based compensation	$ (56)	$ (64)	$ 0
Net excess tax benefits from stock-based compensation, percent	(0.70%)	(1.60%)	0.00%
U.S. deferred tax rate change	$ (154)	$ 596	$ 0
U.S. deferred tax rate change (as a percent)	(2.00%)	14.60%	0.00%
Mandatory deemed repatriation of non-U.S. earnings	$ 50	$ 1,775	$ 0
Mandatory deemed repatriation of non-U.S. earnings (as a percent)	0.70%	43.50%	0.00%
Valuation allowances	$ (29)	$ (111)	$ 141
Valuation allowances (as a percent)	(0.40%)	(2.70%)	101.40%
Nondeductible goodwill	$ 0	$ 0	$ 191
Nondeductible goodwill (as a percent)	0.00%	0.00%	137.40%
Other-net	$ 25	$ 14	$ (14)
Other-net (as a percent)	0.30%	0.30%	(10.10%)
Provision (benefit) for income taxes	$ 1,698	$ 3,339	$ 192
Provision (benefit) for income taxes (as a percent)	21.70%	81.80%	137.80%
U.S. state taxing jurisdictions
(Decreases) increases in taxes resulting from:
Valuation allowances		$ (111)	$ 141