Borrowings - Long-Term Debt, Components (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Borrowings
Long-term debt, gross	$ 43,450	$ 45,445
Less: net unamortized discount	808	826
Less: net unamortized debt issuance cost	79	93
Add: fair value adjustment	198	526
Long-term debt (including current maturities)	42,762	45,052
Less: current maturities	6,773	5,214
Long-term debt (excluding current portion)	35,989	39,837
IBM International Group Capital, LLC
Borrowings
Long-term debt, gross	$ 0
IBM International Group Capital, LLC
Borrowings
Ownership interest in subsidiary (as a percent)	100.00%
U.S. dollars
Borrowings
Long-term debt, gross	$ 30,192	31,515
Euros
Borrowings
Long-term debt, gross	$ 10,162	10,502
Debt instrument, weighted-average interest rate (as a percent)	1.50%
Pound sterling
Borrowings
Long-term debt, gross	$ 1,369	1,420
Debt instrument, weighted-average interest rate (as a percent)	2.70%
Japanese yen
Borrowings
Long-term debt, gross	$ 1,281	1,291
Debt instrument, weighted-average interest rate (as a percent)	0.30%
Other
Borrowings
Long-term debt, gross	$ 446	717
Debt instrument, weighted-average interest rate (as a percent)	6.60%
Maturing 2018 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 1,634	4,640
Debt instrument, weighted-average interest rate (as a percent)	7.60%
Maturing 2019 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 5,474	5,540
Debt instrument, weighted-average interest rate (as a percent)	2.90%
Maturing 2020 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 3,347	3,416
Debt instrument, weighted-average interest rate (as a percent)	2.20%
Maturing 2021 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 5,001	4,129
Debt instrument, weighted-average interest rate (as a percent)	2.50%
Maturing 2022 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 3,533	3,481
Debt instrument, weighted-average interest rate (as a percent)	2.40%
Maturing 2023 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 2,395	1,547
Debt instrument, weighted-average interest rate (as a percent)	3.30%
Maturing 2024 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 2,013	2,000
Debt instrument, weighted-average interest rate (as a percent)	3.60%
Maturing 2025 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 600	600
Debt instrument, weighted-average interest rate (as a percent)	7.00%
Maturing 2026 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 1,350	1,350
Debt instrument, weighted-average interest rate (as a percent)	3.50%
Maturing 2027 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 969	969
Debt instrument, weighted-average interest rate (as a percent)	4.70%
Maturing 2028 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 313	313
Debt instrument, weighted-average interest rate (as a percent)	6.50%
Maturing 2030 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 32
Debt instrument, weighted-average interest rate (as a percent)	3.70%
Maturing 2032 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 600	600
Debt instrument, weighted-average interest rate (as a percent)	5.90%
Maturing 2038 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 83	83
Debt instrument, weighted-average interest rate (as a percent)	8.00%
Maturing 2039 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 745	745
Debt instrument, weighted-average interest rate (as a percent)	5.60%
Maturing 2042 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 1,107	1,107
Debt instrument, weighted-average interest rate (as a percent)	4.00%
Maturing 2045 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 27	27
Debt instrument, weighted-average interest rate (as a percent)	7.00%
Maturing 2046 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 650	650
Debt instrument, weighted-average interest rate (as a percent)	4.70%
Maturing 2096 \| U.S. dollars
Borrowings
Long-term debt, gross	$ 316	316
Debt instrument, weighted-average interest rate (as a percent)	7.10%
Debt securities issued in 2017 \| IBM Credit LLC
Borrowings
Fixed and floating rate debt securities issued		$ 3,000
Debt securities issued during first quarter of 2018 \| IBM Credit LLC
Borrowings
Fixed and floating rate debt securities issued	$ 2,000

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.

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