Segments: (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Segment Information
Pre-tax income	$ 3,606	$ 3,836	[1]
Total segments
Segment Information
External revenue	23,266	24,511
Internal revenue	1,919	1,951
Total revenue reportable segments	25,185	26,462
Pre-tax income	4,435	4,434
Revenue year-to-year change (as a percent)	(4.80%)
Pre-tax income year-to-year change (as a percent)	0.00%
Pre-tax income margin (as a percent)	17.60%	16.80%
Global Technology Services
Segment Information
External revenue	9,605	10,035
Internal revenue	248	293
Total revenue reportable segments	9,852	10,328
Pre-tax income	1,585	1,480
Revenue year-to-year change (as a percent)	(4.60%)
Pre-tax income year-to-year change (as a percent)	7.10%
Pre-tax income margin (as a percent)	16.10%	14.30%
Global Business Services
Segment Information
External revenue	4,484	4,637
Internal revenue	180	182
Total revenue reportable segments	4,664	4,820
Pre-tax income	703	601
Revenue year-to-year change (as a percent)	(3.20%)
Pre-tax income year-to-year change (as a percent)	17.00%
Pre-tax income margin (as a percent)	15.10%	12.50%
Software
Segment Information
External revenue	5,572	5,600
Internal revenue	831	840
Total revenue reportable segments	6,403	6,439
Pre-tax income	2,014	1,945
Revenue year-to-year change (as a percent)	(0.60%)
Pre-tax income year-to-year change (as a percent)	3.50%
Pre-tax income margin (as a percent)	31.50%	30.20%
Systems and Technology
Segment Information
External revenue	3,106	3,749
Internal revenue	120	151
Total revenue reportable segments	3,226	3,900
Pre-tax income	(405)	(105)
Revenue year-to-year change (as a percent)	(17.30%)
Pre-tax income year-to-year change (as a percent)	(286.70%)
Pre-tax income margin (as a percent)	(12.50%)	(2.70%)
Global Financing
Segment Information
External revenue	499	490
Internal revenue	541	485
Total revenue reportable segments	1,040	975
Pre-tax income	$ 538	$ 512
Revenue year-to-year change (as a percent)	6.70%
Pre-tax income year-to-year change (as a percent)	5.00%
Pre-tax income margin (as a percent)	51.80%	52.60%

[1] Amounts may not add due to rounding.