Financing Receivables - Past Due (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Past Due Financing Receivable
Amortized Cost	$ 14,096	$ 18,242
Client Financing Receivables
Past Due Financing Receivable
Amortized Cost	13,077	15,822
Impaired financing receivables, related allowance	167	178
Client Financing Receivables \| Total Past Due > 90 days
Past Due Financing Receivable
Amortized Cost	479	456
Amortized Cost > 90 Days and Accruing	276	241
Billed Invoices > 90 Days and Accruing	16	20
Client Financing Receivables \| Past Due
Past Due Financing Receivable
Amortized Cost Not Accruing	210	223
Client Financing Receivables \| Due Current and Past Due
Past Due Financing Receivable
Amortized Cost	13,077	15,822
Client Financing Receivables \| Americas
Past Due Financing Receivable
Amortized Cost	6,538	7,758
Client Financing Receivables \| Americas \| Total Past Due > 90 days
Past Due Financing Receivable
Amortized Cost	343	295
Amortized Cost > 90 Days and Accruing	251	200
Billed Invoices > 90 Days and Accruing	9	12
Client Financing Receivables \| Americas \| Past Due
Past Due Financing Receivable
Amortized Cost Not Accruing	95	96
Client Financing Receivables \| Americas \| Due Current and Past Due
Past Due Financing Receivable
Amortized Cost	6,538	7,758
Client Financing Receivables \| EMEA
Past Due Financing Receivable
Amortized Cost	4,039	5,023
Client Financing Receivables \| EMEA \| Total Past Due > 90 days
Past Due Financing Receivable
Amortized Cost	103	119
Amortized Cost > 90 Days and Accruing	15	28
Billed Invoices > 90 Days and Accruing	4	5
Client Financing Receivables \| EMEA \| Past Due
Past Due Financing Receivable
Amortized Cost Not Accruing	92	95
Client Financing Receivables \| EMEA \| Due Current and Past Due
Past Due Financing Receivable
Amortized Cost	4,039	5,023
Client Financing Receivables \| Asia Pacific
Past Due Financing Receivable
Amortized Cost	2,500	3,042
Client Financing Receivables \| Asia Pacific \| Total Past Due > 90 days
Past Due Financing Receivable
Amortized Cost	33	42
Amortized Cost > 90 Days and Accruing	10	12
Billed Invoices > 90 Days and Accruing	3	4
Client Financing Receivables \| Asia Pacific \| Past Due
Past Due Financing Receivable
Amortized Cost Not Accruing	23	32
Client Financing Receivables \| Asia Pacific \| Due Current and Past Due
Past Due Financing Receivable
Amortized Cost	$ 2,500	$ 3,042

Billed invoices in financing receivables that are 90 days or more past due and still accruing.

No definition available.

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Namespace Prefix:	ibm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of financing receivable 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
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+ Details

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Balance Type:	debit
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- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
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+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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+ Details

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- Details

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- Details

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