Intangible Assets Including Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020
Changes in Goodwill Balances
Beginning Balance	$ 59,617	$ 58,222
Goodwill Additions	2,351	575
Purchase Price Adjustments	(3)
Divestitures	(13)
Foreign Currency Translation and Other Adjustments	(575)	960
Ending Balance	61,378	59,617
Goodwill impairment losses	0	0
Goodwill accumulated impairment losses	0	0
Red Hat, Inc.
Changes in Goodwill Balances
Purchase Price Adjustments		(139)
Global Technology Services \| Infrastructure Services
Changes in Goodwill Balances
Ending Balance	5,800
Business Segments \| Cloud & Cognitive Software
Changes in Goodwill Balances
Beginning Balance	43,934	43,037
Goodwill Additions	1,655	362
Purchase Price Adjustments	8
Divestitures	(13)
Foreign Currency Translation and Other Adjustments	(374)	675
Ending Balance	45,210	43,934
Business Segments \| Cloud & Cognitive Software \| Red Hat, Inc.
Changes in Goodwill Balances
Purchase Price Adjustments		(139)
Business Segments \| Global Business Services
Changes in Goodwill Balances
Beginning Balance	6,145	5,775
Goodwill Additions	695	205
Purchase Price Adjustments	(11)
Foreign Currency Translation and Other Adjustments	(101)	165
Ending Balance	6,727	6,145
Business Segments \| Global Technology Services
Changes in Goodwill Balances
Beginning Balance	7,245	7,141
Goodwill Additions	2
Foreign Currency Translation and Other Adjustments	(92)	104
Ending Balance	7,155	7,245
Business Segments \| Systems
Changes in Goodwill Balances
Beginning Balance	2,293	2,270
Goodwill Additions		8
Purchase Price Adjustments	0
Foreign Currency Translation and Other Adjustments	(7)	15
Ending Balance	$ 2,286	$ 2,293

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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