Retirement-Related Benefits - Nonpension Postretirement Cost (Details) - Nonpension Postretirement Plans - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
U.S.
Retirement-related plans cost
Service cost	$ 3	$ 4	$ 7	$ 9
Interest cost	38	41	77	82
Amortization of prior service costs/(credits)	(2)	(2)	(4)	(4)
Recognized actuarial losses	5	5	10	10
Total net periodic pension / nonpension (income)/cost of defined benefit plans	45	49	90	97
Non-US
Retirement-related plans cost
Service cost	1	1	3	3
Interest cost	14	11	29	22
Expected return on plan assets	(2)	(2)	(4)	(3)
Amortization of prior service costs/(credits)	0	(1)	0	(2)
Recognized actuarial losses	2	2	3	4
Curtailments and settlements	0		0	0
Total net periodic pension / nonpension (income)/cost of defined benefit plans	$ 16	$ 12	$ 31	$ 23