Segments: (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012		Jun. 30, 2013	Jun. 30, 2012
Segment Information
Revenue	$ 24,924	$ 25,783	[1]	$ 48,332	$ 50,456
Pre-tax income	4,144	5,161		7,750	8,997
Global Technology Services
Segment Information
Revenue	9,536	9,995		19,140	20,031
Global Business Services
Segment Information
Revenue	4,606	4,667		9,091	9,304
Software
Segment Information
Revenue	6,423	6,171		11,995	11,770
Systems and Technology
Segment Information
Revenue	3,758	4,259		6,864	8,008
Global Financing
Segment Information
Revenue	487	517		985	1,006
Total Segments
Segment Information
Revenue	24,809	25,608		48,075	50,120
Business Segments
Segment Information
Revenue	26,737	27,529		51,922	53,991
Pre-tax income	4,989	5,814		9,425	10,248
Revenue year-to-year change (as a percent)	(2.90%)			(3.80%)
Pre-tax income year-to-year change (as a percent)	(14.20%)			(8.00%)
Pre-tax income margin (as a percent)	18.70%	21.10%		18.20%	19.00%
Business Segments | Global Technology Services
Segment Information
Revenue	9,828	10,286		19,680	20,615
Pre-tax income	1,514	1,757		3,099	3,237
Revenue year-to-year change (as a percent)	(4.50%)			(4.50%)
Pre-tax income year-to-year change (as a percent)	(13.80%)			(4.30%)
Pre-tax income margin (as a percent)	15.40%	17.10%		15.70%	15.70%
Business Segments | Global Business Services
Segment Information
Revenue	4,795	4,847		9,459	9,667
Pre-tax income	623	803		1,326	1,404
Revenue year-to-year change (as a percent)	(1.10%)			(2.20%)
Pre-tax income year-to-year change (as a percent)	(22.40%)			(5.60%)
Pre-tax income margin (as a percent)	13.00%	16.60%		14.00%	14.50%
Business Segments | Software
Segment Information
Revenue	7,161	6,946		13,563	13,386
Pre-tax income	2,443	2,493		4,457	4,438
Revenue year-to-year change (as a percent)	3.10%			1.30%
Pre-tax income year-to-year change (as a percent)	(2.00%)			0.40%
Pre-tax income margin (as a percent)	34.10%	35.90%		32.90%	33.20%
Business Segments | Systems and Technology
Segment Information
Revenue	3,893	4,418		7,118	8,317
Pre-tax income	(141)	234		(546)	130
Revenue year-to-year change (as a percent)	(11.90%)			(14.40%)
Pre-tax income margin (as a percent)	(3.60%)	5.30%		(7.70%)	1.60%
Business Segments | Global Financing
Segment Information
Revenue	1,061	1,032		2,101	2,006
Pre-tax income	550	528		1,088	1,040
Revenue year-to-year change (as a percent)	2.90%			4.70%
Pre-tax income year-to-year change (as a percent)	4.20%			4.60%
Pre-tax income margin (as a percent)	51.80%	51.10%		51.80%	51.80%
Internal transactions
Segment Information
Revenue	1,928	1,921		3,847	3,872
Pre-tax income	(379)	(343)		(718)	(627)
Internal transactions | Global Technology Services
Segment Information
Revenue	292	291		540	584
Internal transactions | Global Business Services
Segment Information
Revenue	188	180		368	363
Internal transactions | Software
Segment Information
Revenue	738	776		1,569	1,615
Internal transactions | Systems and Technology
Segment Information
Revenue	135	159		255	309
Internal transactions | Global Financing
Segment Information
Revenue	$ 575	$ 515		$ 1,116	$ 1,000

[1] Amounts may not add due to rounding.