Retirement-Related Benefits - Cost of Pension Plans (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2012	Sep. 30, 2017	Sep. 30, 2016
Cost/(Income) of Pension Plans
Total defined benefit and contribution plans cost recognized in the Consolidated Statement of Earnings	$ 592	$ 421		$ 1,915	$ 1,315
U.S.
Cost/(Income) of Pension Plans
Total defined benefit and contribution plans cost recognized in the Consolidated Statement of Earnings	219	79		665	246
U.S. | Pension Plans
Cost/(Income) of Pension Plans
Interest cost	478	512		1,435	1,536
Expected return on plan assets	(753)	(922)		(2,260)	(2,767)
Amortization of prior service costs/(credits)	4	3		12	8
Recognized actuarial losses	334	328		1,003	985
Total net periodic pension / nonpension (income)/cost of defined benefit plans	63	(79)		190	(238)
Cost of defined contribution plans	156	159		475	484
Non-US
Cost/(Income) of Pension Plans
Total defined benefit and contribution plans cost recognized in the Consolidated Statement of Earnings	373	342		1,250	1,069
Non-US | Pension Plans
Cost/(Income) of Pension Plans
Service cost	106	108		308	318
Interest cost	215	257		622	787
Expected return on plan assets	(340)	(468)		(985)	(1,419)
Amortization of prior service costs/(credits)	(25)	(28)		(73)	(79)
Recognized actuarial losses	387	357		1,120	1,062
Curtailments and settlements	2	4		3	19
Multi-employer plans/other	(74)	8		(46)	64
Total net periodic pension / nonpension (income)/cost of defined benefit plans	271	239		950	751
Cost of defined contribution plans	102	$ 103		301	$ 318
Non-US | Pension Plans | Litigation in United Kingdom regarding defined benefit plans | SG&A expense
Cost/(Income) of Pension Plans
Multi-employer plans/other	$ (91)		$ 162	$ (91)