Retirement-Related Benefits - Cost of Pension Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Cost/(Income) of Pension Plans
Total defined benefit and contribution plans cost recognized in the Consolidated Statement of Earnings	$ 659	$ 455	$ 1,323	$ 894
U.S.
Cost/(Income) of Pension Plans
Total defined benefit and contribution plans cost recognized in the Consolidated Statement of Earnings	218	76	446	167
U.S. | Pension Plans
Cost/(Income) of Pension Plans
Interest cost	478	511	957	1,024
Expected return on plan assets	(753)	(922)	(1,507)	(1,845)
Amortization of prior service costs/(credits)	4	3	8	5
Recognized actuarial losses	331	324	668	657
Total net periodic pension / nonpension (income)/cost of defined benefit plans	60	(85)	127	(158)
Cost of defined contribution plans	158	161	319	326
Non-US
Cost/(Income) of Pension Plans
Total defined benefit and contribution plans cost recognized in the Consolidated Statement of Earnings	442	379	877	727
Non-US | Pension Plans
Cost/(Income) of Pension Plans
Service cost	101	106	202	210
Interest cost	206	267	406	529
Expected return on plan assets	(327)	(481)	(644)	(951)
Amortization of prior service costs/(credits)	(24)	(27)	(48)	(52)
Recognized actuarial losses	371	359	733	706
Curtailments and settlements	3	10	1	14
Multi-employer plans/other costs	14	37	29	55
Total net periodic pension / nonpension (income)/cost of defined benefit plans	344	271	679	512
Cost of defined contribution plans	$ 97	$ 108	$ 198	$ 215