Derivative Financial Instruments - Derivatives, Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
The Effect of Derivative Instruments in the Consolidated Income Statement
Gain/(Loss) Recognized in Earnings, Recognized on Derivatives	$ 8	$ 32	$ 60	$ 52
Gain/(Loss) Recognized in Earnings, Attributable to Risk Being Hedged	(1)	(37)	(49)	(62)
Gains (losses) excluded from the assessment of hedge effectiveness for fair value hedges
Net investment hedges
The Effect of Derivative Instruments in the Consolidated Income Statement
Gain (Loss) Recognized in Earnings and Other Comprehensive Income - Recognized in OCI	(56)	(8)	11	(18)
Gain (Loss) Recognized in Earnings and Other Comprehensive Income - Amounts Excluded from Effectiveness Testing	2	7	9	17
Interest rate contracts \| IBM \| Fair value hedges \| Financing cost
The Effect of Derivative Instruments in the Consolidated Income Statement
Gain/(Loss) Recognized in Earnings, Recognized on Derivatives	8	32	60	52
Gain/(Loss) Recognized in Earnings, Attributable to Risk Being Hedged	(1)	(37)	(49)	(62)
Foreign exchange contracts \| IBM \| Net investment hedges
The Effect of Derivative Instruments in the Consolidated Income Statement
Gain (Loss) Recognized in Earnings and Other Comprehensive Income - Recognized in OCI	(56)	(8)	11	(18)
Foreign exchange contracts \| IBM \| Net investment hedges \| Financing cost
The Effect of Derivative Instruments in the Consolidated Income Statement
Gain (Loss) Recognized in Earnings and Other Comprehensive Income - Amounts Excluded from Effectiveness Testing	$ 2	$ 7	$ 9	$ 17

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

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Amount of gain (loss) from excluded component of derivative hedge, recognized in earnings. Excludes recognition under systematic and rational method.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Net gain (loss) relating to components of the gain (loss) on the fair value hedging instrument excluded from the assessment of fair value hedge effectiveness. Recognized in earnings.

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Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent.

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