Equity Activity (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Equity
Equity, beginning balance			$ 23,172	$ 22,755
Net income	3,839	3,589	10,365	9,576	[1]
Other comprehensive income/(loss) - net of tax
Foreign currency translation adjustments	(1,592)	1,409	(668)	327
Net change in retirement-related benefit plans	300	167	1,241	559
Net unrealized gains/(losses) on marketable securities	(9)	56	(154)	50
Net unrealized gains/(losses) on cash flow hedge derivatives	312	(599)	225	416
Total other comprehensive income/(loss), net of tax	(989)	1,032	645	1,352
Net income plus other comprehensive income/(loss)	2,850	4,621	11,010	10,927
Cash dividends declared - common stock			(2,593)	(2,369)
Stock transactions related to employee plans - net			2,293	2,870
Other treasury shares purchased - not retired			(11,465)	(11,827)
Changes in noncontrolling interests			(40)	2
Equity, ending balance	22,378	22,359	22,378	22,359
Total IBM Stockholders' Equity
Equity
Equity, beginning balance			23,046	22,637
Net income			10,365	9,576
Other comprehensive income/(loss) - net of tax
Total other comprehensive income/(loss), net of tax			645	1,352
Cash dividends declared - common stock			(2,593)	(2,369)
Stock transactions related to employee plans - net			2,293	2,870
Other treasury shares purchased - not retired			(11,465)	(11,827)
Equity, ending balance	22,291	22,238	22,291	22,238
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			2,139	2,518
Equity, ending balance	47,558	44,328	47,558	44,328
Retained Earnings
Equity
Equity, beginning balance			92,532	80,900
Net income			10,365	9,576
Other comprehensive income/(loss) - net of tax
Cash dividends declared - common stock			(2,593)	(2,369)
Stock transactions related to employee plans - net			(38)	(11)
Equity, ending balance	100,266	88,095	100,266	88,095
Treasury Stock
Equity
Equity, beginning balance			(96,161)	(81,243)
Other comprehensive income/(loss) - net of tax
Stock transactions related to employee plans - net			192	362
Other treasury shares purchased - not retired			(11,465)	(11,827)
Equity, ending balance	(107,434)	(92,707)	(107,434)	(92,707)
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			645	1,352
Equity, ending balance	(18,099)	(17,479)	(18,099)	(17,479)
Non-controlling Interests
Equity
Equity, beginning balance			126	118
Other comprehensive income/(loss) - net of tax
Changes in noncontrolling interests			(40)	2
Equity, ending balance	$ 87	$ 121	$ 87	$ 121

[1] Amounts may not add due to rounding.