Segments: (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Segment Information
Revenue	$ 22,484	$ 23,408
Pre-tax income	2,980	3,606
Global Technology Services
Segment Information
Revenue	9,330	9,605
Global Business Services
Segment Information
Revenue	4,483	4,484
Software
Segment Information
Revenue	5,661	5,572
Systems and Technology
Segment Information
Revenue	2,391	3,106
Global Financing
Segment Information
Revenue	512	499
Total Segments
Segment Information
Revenue	22,376	23,266
Business Segments
Segment Information
Revenue	24,476	25,185
Pre-tax income	3,828	4,435
Business Segments | Global Technology Services
Segment Information
Revenue	9,570	9,852
Pre-tax income	1,345	1,585
Revenue year-to-year change (as a percent)	(2.90%)
Pre-tax income year-to-year change (as a percent)	(15.10%)
Pre-tax income margin (as a percent)	14.10%	16.10%
Business Segments | Global Business Services
Segment Information
Revenue	4,624	4,664
Pre-tax income	628	703
Revenue year-to-year change (as a percent)	(0.90%)
Pre-tax income year-to-year change (as a percent)	(10.60%)
Pre-tax income margin (as a percent)	13.60%	15.10%
Business Segments | Software
Segment Information
Revenue	6,593	6,403
Pre-tax income	1,918	2,014
Revenue year-to-year change (as a percent)	3.00%
Pre-tax income year-to-year change (as a percent)	(4.70%)
Pre-tax income margin (as a percent)	29.10%	31.50%
Business Segments | Systems and Technology
Segment Information
Revenue	2,559	3,226
Pre-tax income	(660)	(405)
Revenue year-to-year change (as a percent)	(20.70%)
Pre-tax income year-to-year change (as a percent)	(63.10%)
Pre-tax income margin (as a percent)	(25.80%)	(12.50%)
Business Segments | Global Financing
Segment Information
Revenue	1,129	1,040
Pre-tax income	596	538
Revenue year-to-year change (as a percent)	8.60%
Pre-tax income year-to-year change (as a percent)	10.70%
Pre-tax income margin (as a percent)	52.80%	51.80%
Business Segments | Total Segments
Segment Information
Revenue	24,476	25,185
Pre-tax income	3,828	4,435
Revenue year-to-year change (as a percent)	(2.80%)
Pre-tax income year-to-year change (as a percent)	(13.70%)
Pre-tax income margin (as a percent)	15.60%	17.60%
Internal transactions
Segment Information
Revenue	(2,099)	(1,919)
Pre-tax income	(524)	(339)
Internal transactions | Global Technology Services
Segment Information
Revenue	(241)	(248)
Internal transactions | Global Business Services
Segment Information
Revenue	(141)	(180)
Internal transactions | Software
Segment Information
Revenue	(932)	(831)
Internal transactions | Systems and Technology
Segment Information
Revenue	(168)	(120)
Internal transactions | Global Financing
Segment Information
Revenue	(617)	(541)
Internal transactions | Total Segments
Segment Information
Revenue	$ (2,099)	$ (1,919)