Intangible Assets Including Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Changes in Goodwill Balances
Beginning Balance	$ 59,617	$ 58,222
Goodwill Additions	2,278	575
Purchase Price Adjustments	(6)
Divestitures	(2)
Foreign Currency Translation and Other Adjustments	(242)	960
Ending Balance	61,645	59,617
Goodwill impairment losses	0	0
Goodwill accumulated impairment losses	0	0
Red Hat, Inc.
Changes in Goodwill Balances
Purchase Price Adjustments		(139)
Business Segments \| Cloud & Cognitive Software
Changes in Goodwill Balances
Beginning Balance	43,934	43,037
Goodwill Additions	1,660	362
Purchase Price Adjustments	6
Divestitures	(2)
Foreign Currency Translation and Other Adjustments	(136)	675
Ending Balance	45,461	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	616	205
Purchase Price Adjustments	(11)
Foreign Currency Translation and Other Adjustments	(43)	165
Ending Balance	6,706	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	(62)	104
Ending Balance	7,184	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	0	15
Ending Balance	$ 2,293	$ 2,293

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