Available-for-sale investments (Fair Values by Classification) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Fair values of available-for-sale investments by classification in the Consolidated Balance Sheets
Cash and cash equivalents	$ 3,795	$ 3,731	$ 4,352	$ 3,805
Marketable securities	26,198	23,295
Other assets — noncurrent	1,712	1,592
Total available-for-sale investments	29,689	26,732
Available-for-sale investments [Member]
Fair values of available-for-sale investments by classification in the Consolidated Balance Sheets
Cash and cash equivalents	3,316	3,293
Other assets — noncurrent	$ 175	$ 144