Available-for-sale investments (Details 1) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Fair values of available-for-sale investments by classification in the Consolidated Balance Sheets
Cash and cash equivalents	$ 5,806	$ 3,257	$ 5,849	$ 6,946
Marketable securities	16,212	20,804
Other assets - noncurrent	1,290	1,133
Total available-for-sale investments	21,654	23,745
Available-for-sale investments [Member]
Fair values of available-for-sale investments by classification in the Consolidated Balance Sheets
Cash and cash equivalents	5,352	2,887
Other assets - noncurrent	$ 90	$ 54