Intangible Assets Including Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Changes in Goodwill Balances
Beginning Balance	$ 59,617	$ 58,222
Goodwill Additions	746	575
Purchase Price Adjustments	6	(139)
Foreign Currency Translation and Other Adjustments	(384)	960
Ending Balance	59,984	59,617
Goodwill impairment losses	0	0
Goodwill accumulated impairment losses	0
Business Segments \| Cloud & Cognitive Software
Changes in Goodwill Balances
Beginning Balance	43,934	43,037
Goodwill Additions	245	362
Purchase Price Adjustments	6	(139)
Foreign Currency Translation and Other Adjustments	(249)	675
Ending Balance	43,935	43,934
Business Segments \| Global Business Services
Changes in Goodwill Balances
Beginning Balance	6,145	5,775
Goodwill Additions	501	205
Purchase Price Adjustments	0
Foreign Currency Translation and Other Adjustments	(61)	165
Ending Balance	6,585	6,145
Business Segments \| Global Technology Services
Changes in Goodwill Balances
Beginning Balance	7,245	7,141
Foreign Currency Translation and Other Adjustments	(70)	104
Ending Balance	7,175	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	(4)	15
Ending Balance	$ 2,289	$ 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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