Retirement-Related Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012		Sep. 30, 2013	Sep. 30, 2012
Retirement-related plans cost
Defined benefit and contribution pension plan - cost	$ 631	$ 612		$ 1,941	$ 1,602
Nonpension postretirement plans - cost	74	86		224	260
Total	705	698		2,165	1,862
Year-to-year percent change, defined benefit and contribution pension plans cost	3.10%			21.10%
Year-to-year percent change, Nonpension postretirement plans cost	(14.00%)			(13.60%)
Year-to-year percent change, total	1.00%			16.30%
Defined benefit and contribution pension plan - cost U.S. Plans	154	82		452	305
Defined benefit and contribution pension plan - cost Non U.S. Plans	478	530		1,489	1,297
Proceeds from Medicare Prescription Drug Improvement and Modernization Act of 2003	8.2			24.4
Litigation in United Kingdom regarding defined benefit plans (C Plan)
Retirement-related plans cost
Multi-employer plans/other costs		162			162
U.S. Defined Benefit Pension Plans
Retirement-related plans cost
Interest cost	495	549		1,485	1,647
Expected return on plan assets	(995)	(1,011)		(2,986)	(3,033)
Amortization of prior service costs/(credits)	2	2		7	7
Recognized actuarial losses	448	333		1,343	998
Total net periodic pension (income)/cost of defined benefit plans	(50)	(127)		(151)	(381)
Cost of defined contribution plans	204	209		603	686
Non-US Defined Benefit Pension Plans
Retirement-related plans cost
Service cost	124	109		375	332
Interest cost	379	439		1,137	1,332
Expected return on plan assets	(546)	(570)		(1,636)	(1,723)
Amortization of prior service costs/(credits)	(29)	(39)		(90)	(116)
Recognized actuarial losses	397	255		1,195	770
Curtailments and settlements	0	0			1
Multi-employer plans/other costs	16	188	[1]	71	234	[1]
Total net periodic pension (income)/cost of defined benefit plans	341	381		1,052	831
Cost of defined contribution plans	137	148		437	467
Non-U.S. Defined Benefit and Multi-employer Plan
Retirement-related plans cost
Expected current year contributions to non-U.S. defined benefit plans				500
Year-to-date contributions to non-U.S. defined benefit plans				397
U.S. Defined Benefit Non Pension Postretirement Plans
Retirement-related plans cost
Service cost	9	9		26	28
Interest cost	41	50		123	150
Expected return on plan assets	0			(1)
Recognized actuarial losses	5	8		16	24
Total net periodic pension (income)/cost of defined benefit plans	55	67		164	201
Non-U.S. Defined Benefit Non Pension Postretirement Plans
Retirement-related plans cost
Service cost	2	2		7	7
Interest cost	14	16		46	48
Expected return on plan assets	(2)	(2)		(7)	(7)
Amortization of prior service costs/(credits)	(1)	(1)		(4)	(3)
Recognized actuarial losses	6	4		18	13
Curtailments and settlements				0
Total net periodic pension (income)/cost of defined benefit plans	$ 19	$ 19		$ 60	$ 58

[1] *Includes a $162 million charge related to litigation involving one of IBM UK’s defined benefit plans.