Financing arrangements (Details 1) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule of 2013 convertible notes
Principal balance	$ 10,500	$ 2,500	$ 2,000
0.375% convertible notes due 2013 (0.375% 2013 Convertible Notes) [Member]
Schedule of 2013 convertible notes
Principal balance	2,500
Net carrying amount	2,346	2,213
0.375% convertible notes due 2013 (0.375% 2013 Convertible Notes) [Member] | Liability component [Member]
Schedule of 2013 convertible notes
Principal balance	2,500	2,500
Unamortized discount	154	287
Net carrying amount	2,346	2,213
0.375% convertible notes due 2013 (0.375% 2013 Convertible Notes) [Member] | Equity component [Member]
Schedule of 2013 convertible notes
Net carrying amount	$ 829	$ 829