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)			2,422		(2,422)
Net income plus other comprehensive income/(loss):
Net income	4,083		4,083				4,083
Other comprehensive income/(loss)	724				724		724
Total comprehensive income/(loss)	4,807						4,807
Cash dividends paid - common stock	(2,819)		(2,819)				(2,819)
Common stock issued under employee plans	261	261					261
Purchases and sales of treasury stock under employee plans - net	(86)		12	(98)			(86)
Other treasury shares purchased, not retired	(1,761)			(1,761)			(1,761)
Changes in noncontrolling interests						(3)	(3)
Balance at the End of the Period at Jun. 30, 2018	18,520	54,827	157,349	(165,366)	(28,290)	128	18,648
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 Mar. 31, 2018	18,166	54,712	156,371	(164,334)	(28,583)	124	18,290
Net income plus other comprehensive income/(loss):
Net income	2,404		2,404				2,404
Other comprehensive income/(loss)	294				294		294
Total comprehensive income/(loss)	2,697						2,697
Cash dividends paid - common stock	(1,437)		(1,437)				(1,437)
Common stock issued under employee plans	115	115					115
Purchases and sales of treasury stock under employee plans - net	(41)		10	(51)			(41)
Other treasury shares purchased, not retired	(980)			(980)			(980)
Changes in noncontrolling interests						3	3
Balance at the End of the Period at Jun. 30, 2018	18,520	54,827	157,349	(165,366)	(28,290)	128	18,648
Balance at the Beginning 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	4,089		4,089				4,089
Other comprehensive income/(loss)	649				649		649
Total comprehensive income/(loss)	4,738						4,738
Cash dividends paid - common stock	(2,833)		(2,833)				(2,833)
Common stock issued under employee plans	254	254					254
Purchases and sales of treasury stock under employee plans - net	(88)		11	(99)			(88)
Other treasury shares purchased, not retired	(1,216)			(1,216)			(1,216)
Changes in other equity	(5)		(5)				(5)
Changes in noncontrolling interests						(3)	(3)
Balance at the End of the Period at Jun. 30, 2019	17,645	55,404	160,467	(169,385)	(28,841)	131	17,776
Balance at the Beginning of the Period at Mar. 31, 2019	16,481	55,287	159,396	(169,021)	(29,182)	126	16,607
Net income plus other comprehensive income/(loss):
Net income	2,498		2,498				2,498
Other comprehensive income/(loss)	340				340		340
Total comprehensive income/(loss)	2,839						2,839
Cash dividends paid - common stock	(1,435)		(1,435)				(1,435)
Common stock issued under employee plans	117	117					117
Purchases and sales of treasury stock under employee plans - net	(40)		9	(49)			(40)
Other treasury shares purchased, not retired	(316)			(316)			(316)
Changes in noncontrolling interests						5	5
Balance at the End of the Period at Jun. 30, 2019	$ 17,645	$ 55,404	$ 160,467	$ (169,385)	$ (28,841)	$ 131	$ 17,776