Retirement-Related Benefits - Nonpension Postretirement Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
U.S. Defined Benefit Non Pension Postretirement Plans
Retirement-related plans cost
Service cost	$ 4	$ 6	$ 9	$ 12
Interest cost	41	40	82	82
Expected return on plan assets		0		0
Amortization of prior service costs/(credits)	(2)	(2)	(4)	(4)
Recognized actuarial losses	5	9	10	20
Curtailments and settlements		0		0
Total net periodic pension / nonpension (income)/cost of defined benefit plans	49	53	97	109
Non-U.S. Defined Benefit Non Pension Postretirement Plans
Retirement-related plans cost
Service cost	1	2	3	4
Interest cost	11	13	22	27
Expected return on plan assets	(2)	(2)	(3)	(4)
Amortization of prior service costs/(credits)	(1)	(1)	(2)	(3)
Recognized actuarial losses	2	2	4	5
Curtailments and settlements		0	0	0
Total net periodic pension / nonpension (income)/cost of defined benefit plans	$ 12	$ 14	$ 23	$ 29