CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (Parenthetical)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
CONSOLIDATED STATEMENT OF CHANGES IN EQUITY
Common stock issued under employee plans (in shares)	2,125,560	3,105,227
Purchases of treasury stock under employee plans (in shares)	363,779	488,203
Sales of treasury stock under employee plans (in shares)	187,271	328,673
Other treasury shares purchased, not retired (in shares)	7,738,744us-gaap_TreasuryStockSharesAcquired	45,153,202us-gaap_TreasuryStockSharesAcquired

Aggregate change in shares for common stock issued during the period related to all employee plans.

No definition available.

Name:	ibm_CommonStockIssuedUnderEmployeePlanShares
Namespace Prefix:	ibm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Change in shares of treasury stock related to purchases under employee plan transactions including shares tendered for tax.

+ References

No definition available.

+ Details

Name:	ibm_PurchasesTreasuryStockUnderEmployeePlansShares
Namespace Prefix:	ibm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of treasury shares (units) reissued during the period, used to satisfy equity-based compensation obligations exercised by the holders of such rights.

+ References

No definition available.

+ Details

Name:	ibm_SalesTreasuryStockUnderEmployeePlansShares
Namespace Prefix:	ibm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementOfStockholdersEquityAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares that have been repurchased during the period and are being held in treasury.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

+ Details

Name:	us-gaap_TreasuryStockSharesAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration