Segments: (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Segment Information
Pre-tax income	$ 3,836	[1]	$ 3,817
Total segments
Segment Information
External revenue	24,511		24,416
Internal revenue	1,951		2,078
Total revenue reportable segments	26,462		26,494
Pre-tax income	4,434		4,264
Revenue year-to-year change (as a percent)	(0.10%)
Pre-tax income year-to-year change (as a percent)	4.00%
Pre-tax income margin (as a percent)	16.80%		16.10%
Global Technology Services
Segment Information
External revenue	10,035		9,863
Internal revenue	293		307
Total revenue reportable segments	10,328		10,170
Pre-tax income	1,480		1,238
Revenue year-to-year change (as a percent)	1.60%
Pre-tax income year-to-year change (as a percent)	19.60%
Pre-tax income margin (as a percent)	14.30%		12.20%
Global Business Services
Segment Information
External revenue	4,637		4,710
Internal revenue	182		200
Total revenue reportable segments	4,820		4,910
Pre-tax income	601		640
Revenue year-to-year change (as a percent)	(1.80%)
Pre-tax income year-to-year change (as a percent)	(6.10%)
Pre-tax income margin (as a percent)	12.50%		13.00%
Software
Segment Information
External revenue	5,600		5,308
Internal revenue	840		830
Total revenue reportable segments	6,439		6,138
Pre-tax income	1,945		1,735
Revenue year-to-year change (as a percent)	4.90%
Pre-tax income year-to-year change (as a percent)	12.10%
Pre-tax income margin (as a percent)	30.20%		28.30%
Systems and Technology
Segment Information
External revenue	3,749		4,019
Internal revenue	151		244
Total revenue reportable segments	3,900		4,263
Pre-tax income	(105)		132
Revenue year-to-year change (as a percent)	(8.50%)
Pre-tax income margin (as a percent)	(2.70%)		3.10%
Global Financing
Segment Information
External revenue	490		516
Internal revenue	485		497
Total revenue reportable segments	975		1,013
Pre-tax income	$ 512		$ 519
Revenue year-to-year change (as a percent)	(3.80%)
Pre-tax income year-to-year change (as a percent)	(1.30%)
Pre-tax income margin (as a percent)	52.60%		51.30%

[1] Amounts may not add due to rounding.