Segments: (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Information
Pre-tax income	$ 5,074	[1]	$ 5,027	$ 14,071	$ 13,729
Total segments
Segment Information
External revenue	24,594		25,974	74,713	76,866
Internal revenue	1,976		1,989	5,848	6,148
Total revenue reportable segments	26,570		27,963	80,561	83,015
Pre-tax income	5,389		5,484	15,637	15,118
Revenue year-to-year change (as a percent)	(5.00%)			(3.00%)
Pre-tax income year-to-year change (as a percent)	(1.70%)			3.40%
Pre-tax income margin (as a percent)	20.30%		19.60%	19.40%	18.20%
Global Technology Services
Segment Information
External revenue	9,922		10,322	29,952	30,427
Internal revenue	285		316	869	943
Total revenue reportable segments	10,206		10,638	30,821	31,370
Pre-tax income	1,697		1,695	4,934	4,353
Revenue year-to-year change (as a percent)	(4.10%)			(1.80%)
Pre-tax income year-to-year change (as a percent)	0.10%			13.30%
Pre-tax income margin (as a percent)	16.60%		15.90%	16.00%	13.90%
Global Business Services
Segment Information
External revenue	4,542		4,832	13,846	14,407
Internal revenue	175		199	538	604
Total revenue reportable segments	4,717		5,031	14,384	15,012
Pre-tax income	738		775	2,142	2,166
Revenue year-to-year change (as a percent)	(6.20%)			(4.20%)
Pre-tax income year-to-year change (as a percent)	(4.80%)			(1.10%)
Pre-tax income margin (as a percent)	15.60%		15.40%	14.90%	14.40%
Software
Segment Information
External revenue	5,763		5,817	17,533	17,295
Internal revenue	843		804	2,459	2,425
Total revenue reportable segments	6,606		6,621	19,992	19,720
Pre-tax income	2,355		2,214	6,793	6,260
Revenue year-to-year change (as a percent)	(0.20%)			1.40%
Pre-tax income year-to-year change (as a percent)	6.30%			8.50%
Pre-tax income margin (as a percent)	35.60%		33.40%	34.00%	31.70%
Systems and Technology
Segment Information
External revenue	3,895		4,482	11,903	13,182
Internal revenue	181		190	491	652
Total revenue reportable segments	4,076		4,672	12,394	13,834
Pre-tax income	124		318	253	843
Revenue year-to-year change (as a percent)	(12.80%)			(10.40%)
Pre-tax income year-to-year change (as a percent)	(61.10%)			(70.00%)
Pre-tax income margin (as a percent)	3.00%		6.80%	2.00%	6.10%
Global Financing
Segment Information
External revenue	472		520	1,478	1,555
Internal revenue	491		480	1,492	1,524
Total revenue reportable segments	963		999	2,970	3,078
Pre-tax income	$ 476		$ 481	$ 1,516	$ 1,497
Revenue year-to-year change (as a percent)	(3.60%)			(3.50%)
Pre-tax income year-to-year change (as a percent)	(1.20%)			1.30%
Pre-tax income margin (as a percent)	49.40%		48.20%	51.00%	48.60%

[1] Amounts may not add due to rounding.