Equity Activity (Details) (USD $) In Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Equity
Equity, beginning balance					$ 23,172		$ 22,755
Net income	3,664		3,386	[1]	6,526	[1]	5,987
Other comprehensive income/(loss) - net of tax
Foreign currency translation adjustments	389		(929)		924		(1,081)
Net change in retirement-related benefit plans	634		168		942		392
Net unrealized gains/(losses) on marketable securities	(22)		(47)		(145)		(6)
Net unrealized gains/(losses) on cash flow hedge derivatives	8		475		(87)		1,015
Total other comprehensive income/(loss), net of tax	1,010		(332)		1,634		320
Net income plus other comprehensive income/(loss)	4,673		3,053		8,160		6,306
Cash dividends declared - common stock					(1,700)		(1,551)
Stock transactions related to employee plans - net					1,662		1,899
Other treasury shares purchased - not retired					(8,041)		(8,233)
Changes in noncontrolling interests					(43)		(1)
Equity, ending balance	23,210	[1]	21,176		23,210	[1]	21,176
Total IBM Stockholders' Equity
Equity
Equity, beginning balance					23,046		22,637
Net income					6,526		5,987
Other comprehensive income/(loss) - net of tax
Total other comprehensive income/(loss), net of tax					1,634		320
Cash dividends declared - common stock					(1,700)		(1,551)
Stock transactions related to employee plans - net					1,662		1,899
Other treasury shares purchased - not retired					(8,041)		(8,233)
Equity, ending balance	23,127		21,059		23,127		21,059
Common Stock and Additional Paid-in Capital
Equity
Equity, beginning balance					45,418		41,810
Other comprehensive income/(loss) - net of tax
Stock transactions related to employee plans - net					1,556		1,712
Equity, ending balance	46,975		43,522		46,975		43,522
Retained Earnings
Equity
Equity, beginning balance					92,532		80,900
Net income					6,526		5,987
Other comprehensive income/(loss) - net of tax
Cash dividends declared - common stock					(1,700)		(1,551)
Stock transactions related to employee plans - net					(24)		(12)
Equity, ending balance	97,334		85,323		97,334		85,323
Treasury Stock
Equity
Equity, beginning balance					(96,161)		(81,243)
Other comprehensive income/(loss) - net of tax
Stock transactions related to employee plans - net					129		200
Other treasury shares purchased - not retired					(8,041)		(8,233)
Equity, ending balance	(104,073)		(89,276)		(104,073)		(89,276)
Accumulated Other Comprehensive Income/(Loss)
Equity
Equity, beginning balance					(18,743)		(18,830)
Other comprehensive income/(loss) - net of tax
Total other comprehensive income/(loss), net of tax					1,634		320
Equity, ending balance	(17,109)		(18,510)		(17,109)		(18,510)
Non-controlling Interests
Equity
Equity, beginning balance					126		118
Other comprehensive income/(loss) - net of tax
Changes in noncontrolling interests					(43)		(1)
Equity, ending balance	$ 84		$ 117		$ 84		$ 117

[1] Amounts may not add due to rounding.