Borrowings - Long-Term Debt, Components (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Debt Disclosure
Long-term debt, gross	$ 44,027	$ 38,820
Less: net unamortized discount	853	838
Less: unamortized debt issuance costs	90	74
Add: fair value adjustment	1,140	790
Long-term debt (including current maturities)	44,224	38,699
Less: current maturities	4,586	5,271
Total long-term debt (excluding current portion)	39,638	33,428
IBM International Group Capital, LLC
Debt Disclosure
Long-term debt, gross	$ 0
Ownership interest in subsidiary (as a percent)	100.00%
U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 32,644	30,319
Euros
Debt Disclosure
Long-term debt, gross	$ 7,493	4,892
Debt instrument, average interest rate percentage (as a percent)	1.60%
Pound sterling
Debt Disclosure
Long-term debt, gross	$ 1,400	1,555
Debt instrument, average interest rate percentage (as a percent)	2.70%
Japanese yen
Debt Disclosure
Long-term debt, gross	$ 1,383	1,180
Debt instrument, average interest rate percentage (as a percent)	0.30%
Swiss francs
Debt Disclosure
Long-term debt, gross	$ 8	9
Debt instrument, average interest rate percentage (as a percent)	6.30%
Canadian
Debt Disclosure
Long-term debt, gross	$ 385	360
Debt instrument, average interest rate percentage (as a percent)	2.20%
Other
Debt Disclosure
Long-term debt, gross	$ 715	506
Debt instrument, average interest rate percentage (as a percent)	12.40%
Maturing 2016 Through 2017 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 7,198	9,351
Debt instrument, average interest rate percentage (as a percent)	3.36%
Maturing 2018 Through 2019 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 8,841	7,591
Debt instrument, average interest rate percentage (as a percent)	3.17%
Maturing 2020 Through 2021 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 4,943	3,717
Debt instrument, average interest rate percentage (as a percent)	1.72%
Maturing 2022 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 1,901	1,900
Debt instrument, average interest rate percentage (as a percent)	2.35%
Maturing 2023 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 1,500	1,500
Debt instrument, average interest rate percentage (as a percent)	3.38%
Maturing 2024 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 2,000	2,000
Debt instrument, average interest rate percentage (as a percent)	3.63%
Maturing 2025 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 600	600
Debt instrument, average interest rate percentage (as a percent)	7.00%
Maturing 2026 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 1,350
Debt instrument, average interest rate percentage (as a percent)	3.45%
Maturing 2027 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 469	469
Debt instrument, average interest rate percentage (as a percent)	6.22%
Maturing 2028 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 313	313
Debt instrument, average interest rate percentage (as a percent)	6.50%
Maturing 2032 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 600	600
Debt instrument, average interest rate percentage (as a percent)	5.88%
Maturing 2038 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 83	83
Debt instrument, average interest rate percentage (as a percent)	8.00%
Maturing 2039 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 745	745
Debt instrument, average interest rate percentage (as a percent)	5.60%
Maturing 2042 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 1,107	1,107
Debt instrument, average interest rate percentage (as a percent)	4.00%
Maturing 2045 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 27	27
Debt instrument, average interest rate percentage (as a percent)	7.00%
Maturing 2046 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 650
Debt instrument, average interest rate percentage (as a percent)	4.70%
Maturing 2096 \| U.S. dollars
Debt Disclosure
Long-term debt, gross	$ 316	$ 316
Debt instrument, average interest rate percentage (as a percent)	7.13%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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

- Definition

Amount, after accumulated amortization, of debt discount.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedDiscount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective interest rate fair value hedge that is amortized upon discontinuation of the interest rate fair value hedge.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 35
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=65886642&loc=d3e75592-113984

+ Details

Name:	us-gaap_DeferredGainLossOnDiscontinuationOfInterestRateFairValueHedge
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

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

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

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

- Definition

Weighted average interest rate of long-term debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_LongtermDebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant