Acquisitions/Divestitures (Narratives) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended												9 Months Ended			0 Months Ended
	Sep. 30, 2013 acquisitions	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2013 Software	Dec. 31, 2012 Software	Dec. 31, 2011 Software	Sep. 30, 2013 Global Technology Services	Dec. 31, 2012 Global Technology Services	Dec. 31, 2011 Global Technology Services	Sep. 30, 2013 Systems and Technology	Dec. 31, 2012 Systems and Technology	Dec. 31, 2011 Systems and Technology	Sep. 30, 2013 Other Acquisitions	Sep. 30, 2013 Other Acquisitions Software acquisitions	Sep. 30, 2013 Other Acquisitions Systems and Technology acquisitions	Jul. 03, 2013 SoftLayer Technologies Inc	Sep. 30, 2013 SoftLayer Technologies Inc	Jul. 03, 2013 SoftLayer Technologies Inc Software	Jul. 03, 2013 SoftLayer Technologies Inc Global Technology Services
Business Acquisition [Line Items]
Businesses acquired, number (in entities)	7													5	1
Businesses acquired, aggregate cost	$ 2,734
Acquired intangible asset, weighted average useful life													6 years 6 months			7 years
Expected percent of goodwill deductible for tax purposes													3.00%			0.00%
Total purchase price													757			1,977	1,977
Goodwill	$ 30,882	$ 29,247	$ 26,213	$ 20,818	$ 20,405	$ 18,121	$ 4,126	$ 2,916	$ 2,646	$ 1,607	$ 1,568	$ 1,133	$ 551	$ 538	$ 13	$ 1,284	$ 1,284	$ 39	$ 1,245
Percentage of business acquired														100.00%	100.00%	100.00%