CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Millions		Total IBM Stockholders' Equity	Common Stock and Additional Paid-in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income/(Loss)	Non-Controlling Interests	Total
Balance at the Beginning of the Period at Dec. 31, 2017		$ 17,594	$ 54,566	$ 153,126	$ (163,507)	$ (26,592)	$ 131	$ 17,725
Equity
Cumulative effect of change in accounting principle | Accounting Standards Update 2014-09, Revenue from Contracts with Customers		524		524				524
Cumulative effect of change in accounting principle | Accounting Standards Updates 2016-01 (Financial Instruments), 2017-12 (Hedging) and 2018-02 (Stranded Tax Effects)	[1]			2,422		(2,422)
Net income plus other comprehensive income/(loss):
Net income		6,777		6,777				6,777
Other comprehensive income/(loss)		1,194				1,194		1,194
Total comprehensive income/(loss)		7,970						7,970
Cash dividends paid - common stock		(4,250)		(4,250)				(4,250)
Common stock issued under employee plans		421	421					421
Purchases and sales of treasury stock under employee plans - net		(89)		13	(101)			(89)
Other treasury shares purchased, not retired		(2,388)			(2,388)			(2,388)
Changes in noncontrolling interests							3	3
Balance at the End of the Period at Sep. 30, 2018		19,784	54,987	158,612	(165,995)	(27,820)	134	19,918
Balance at the Beginning of the Period at Dec. 31, 2017		17,594	54,566	153,126	(163,507)	(26,592)	131	17,725
Balance at the End of the Period at Dec. 31, 2018		16,796	55,151	159,206	(168,071)	(29,490)	134	16,929
Balance at the Beginning of the Period at Jun. 30, 2018		18,520	54,827	157,349	(165,366)	(28,290)	128	18,648
Net income plus other comprehensive income/(loss):
Net income		2,694		2,694				2,694
Other comprehensive income/(loss)		470				470		470
Total comprehensive income/(loss)		3,164						3,164
Cash dividends paid - common stock		(1,431)		(1,431)				(1,431)
Common stock issued under employee plans		160	160					160
Purchases and sales of treasury stock under employee plans - net		(2)		1	(3)			(2)
Other treasury shares purchased, not retired		(627)			(627)			(627)
Changes in noncontrolling interests							6	6
Balance at the End of the Period at Sep. 30, 2018		19,784	54,987	158,612	(165,995)	(27,820)	134	19,918
Balance at the End of the Period at Dec. 31, 2018		16,796	55,151	159,206	(168,071)	(29,490)	134	16,929
Net income plus other comprehensive income/(loss):
Net income		5,761		5,761				5,761
Other comprehensive income/(loss)		404				404		404
Total comprehensive income/(loss)		6,165						6,165
Cash dividends paid - common stock		(4,269)		(4,269)				(4,269)
Common stock issued under employee plans		657	657					657
Purchases and sales of treasury stock under employee plans - net		(56)		16	(72)			(56)
Other treasury shares purchased, not retired		(1,331)			(1,331)			(1,331)
Changes in other equity		(5)		(5)				(5)
Changes in noncontrolling interests							6	6
Balance at the End of the Period at Sep. 30, 2019		17,956	55,808	160,709	(169,474)	(29,086)	139	18,096
Balance at the Beginning of the Period at Jun. 30, 2019		17,645	55,404	160,467	(169,385)	(28,841)	131	17,776
Net income plus other comprehensive income/(loss):
Net income		1,672		1,672				1,672
Other comprehensive income/(loss)		(245)				(245)		(245)
Total comprehensive income/(loss)		1,427						1,427
Cash dividends paid - common stock		(1,436)		(1,436)				(1,436)
Common stock issued under employee plans		404	404					404
Purchases and sales of treasury stock under employee plans - net		32		6	27			32
Other treasury shares purchased, not retired		(115)			(115)			(115)
Changes in noncontrolling interests							8	8
Balance at the End of the Period at Sep. 30, 2019		$ 17,956	$ 55,808	$ 160,709	$ (169,474)	$ (29,086)	$ 139	$ 18,096

[1] * Reflects the adoption of the FASB guidance on stranded tax effects, hedging and financial instruments. Refer to note 2, “Accounting Changes.”