Subsequent Events (Details) - $ / shares		1 Months Ended
Apr. 30, 2019	Jan. 31, 2019
Subsequent Events
Dividend declared (in dollars per share)		$ 1.57
Subsequent event
Subsequent Events
Dividend declared, date	Apr. 30, 2019
Dividend declared (in dollars per share)	$ 1.62
Dividend payable, date	Jun. 10, 2019
Shareholders of record, date	May 10, 2019
Dividend per share increase (in dollars per share)	$ 0.05
Dividend per share increase (as a percent)	3.00%

Represents the increase in the dividend declared over the prior period.

No definition available.

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Namespace Prefix:	ibm_
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Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage increase in the dividend declared over the prior period.

+ References

No definition available.

+ Details

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Namespace Prefix:	ibm_
Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Aggregate dividends declared during the period for each share of common stock outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the declared dividend will be paid, in CCYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

+ Details

Name:	us-gaap_DividendPayableDateToBePaidDayMonthAndYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the dividend to be paid was declared, in CCYY-MM-DD format.

+ References

+ Details

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Data Type:	xbrli:dateItemType
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Period Type:	duration

- Definition

Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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Period Type:	duration

- Details

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