Intangible Assets Including Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2017	Dec. 31, 2016
Changes in Goodwill Balances
Beginning Balance	$ 36,199	$ 32,021
Goodwill Additions	8	4,244
Purchase Price Adjustments	3	(7)
Divestitures		(18)
Foreign Currency Translation and Other Adjustments	97	(42)
Ending Balance	36,307	36,199
Goodwill impairment losses	0	0
Goodwill accumulated impairment losses	0	0
Cognitive Solutions
Changes in Goodwill Balances
Beginning Balance	19,484	15,621
Goodwill Additions	3	3,821
Purchase Price Adjustments	4	5
Divestitures		(12)
Foreign Currency Translation and Other Adjustments	26	48
Ending Balance	19,518	19,484
Global Business Services
Changes in Goodwill Balances
Beginning Balance	4,607	4,396
Goodwill Additions		303
Purchase Price Adjustments	2	4
Divestitures		(1)
Foreign Currency Translation and Other Adjustments	35	(95)
Ending Balance	4,643	4,607
Technology Services & Cloud Platforms
Changes in Goodwill Balances
Beginning Balance	10,258	10,156
Goodwill Additions	5	119
Purchase Price Adjustments	(3)	(12)
Divestitures		(5)
Foreign Currency Translation and Other Adjustments	35	(1)
Ending Balance	10,295	10,258
Systems
Changes in Goodwill Balances
Beginning Balance	1,850	1,848
Purchase Price Adjustments		(4)
Foreign Currency Translation and Other Adjustments	1	5
Ending Balance	$ 1,851	$ 1,850

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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