RETIREMENT-RELATED BENEFITS - All Retirement Plans Cost (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Retirement-Related Benefits
Total retirement-related benefits net periodic cost	$ 2,003	$ 2,572	$ 1,974
U.S.
Retirement-Related Benefits
Total retirement-related benefits net periodic cost	527	654	115
Non-U.S.
Retirement-Related Benefits
Total retirement-related benefits net periodic cost	1,475	1,918	1,859
IBM 401(k) Plus Plan
Retirement-Related Benefits
Total defined contribution plans cost	626	676	713
Non-US Pension Plans
Retirement-Related Benefits
Total defined contribution plans cost	420	442	526
IBM 401(k) Plus Plan and Non-U.S. Defined Contribution Plans
Retirement-Related Benefits
Total defined contribution plans cost	1,046	1,117	1,239
IBM Excess 401(k) Plus Plan
Retirement-Related Benefits
Total defined contribution plans cost	24	21	14
U.S. Pension Plans
Retirement-Related Benefits
Total defined contribution plans cost	650	697	727
Pension Plans
Retirement-Related Benefits
Total defined contribution plans cost	1,070	1,138	1,253
Personal Pension Plan (PPP)
Retirement-Related Benefits
Total defined benefit plans (income)/cost	(334)	(284)	(833)
Non-US Pension Plans
Retirement-Related Benefits
Total defined benefit plans (income)/cost	1,039	1,421	1,267
PPP and Non-U.S. Defined Benefit Pension Plans
Retirement-Related Benefits
Total defined benefit plans (income)/cost	705	1,137	434
Retention Plan
Retirement-Related Benefits
Total defined benefit plans (income)/cost	17	23	15
U.S. Pension Plans
Retirement-Related Benefits
Total defined benefit plans (income)/cost	(317)	(261)	(818)
Pension Plans
Retirement-Related Benefits
Total defined benefit plans (income)/cost	722	1,160	449
U.S. Nonpension Postretirement Benefit Plans
Retirement-Related Benefits
Total defined benefit plans (income)/cost	195	218	206
Non-U.S. Nonpension Postretirement Benefit Plans
Retirement-Related Benefits
Total defined benefit plans (income)/cost	16	55	66
Nonpension Postretirement Plans
Retirement-Related Benefits
Total defined benefit plans (income)/cost	$ 211	$ 273	$ 272

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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- Definition

The amount of pension and other (such as medical, dental and life insurance) postretirement benefit costs recognized during the period for (1) defined benefit plans (periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss) on assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments) and for (2) defined contribution plans (to the extent that a plan's defined contributions to an individual's account are to be made for periods in which that individual renders services, the net cost for a period is the contribution called for in that period; if a plan calls for contributions for periods after an individual retires or terminates, the estimated cost is accrued during the employee's service period).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.4)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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