Acquisitions/Divestitures - Divestitures (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) entity
Select Standalone Cloud and Cognitive Software Products
Divestitures
Cash consideration	$ 812
Number of divestitures | entity	3
Consideration	$ 1,775
Contingent consideration	150
Cash consideration expected to receive	$ 813
Period after closing for receipt of remaining consideration	12 months
Pre-tax gain on sale of business	$ 556
Select Standalone Cloud and Cognitive Software Products | Maximum
Divestitures
Initial term for transition services	1 year
Select Marketing Platform and Commerce Offerings
Divestitures
Initial term for transition services	9 months
Renewal term for transition services	9 months
Select Marketing Platform and Commerce Offerings | Remaining countries
Divestitures
Period for closing	12 months
Select Marketing Platform and Commerce Offerings | U.S.
Divestitures
Cash consideration	$ 240
Cash consideration expected to receive	$ 150
Period after closing for receipt of remaining consideration	36 months