Acquisitions & Divestitures - 2018 Acquisitions (Details) - 2018 Acquisitions $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($) item
Acquisitions
Number of acquisitions	2
Aggregate acquisitions cost \| $	$ 49
Cloud & Cognitive Software
Acquisitions
Number of acquisitions	1
Global Business Services
Acquisitions
Number of acquisitions	1

Amount of equity interests of the acquirer, including instruments or interests issued or issuable in consideration for the business combination.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477

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