Available-for-sale investments (Fair Values by Classification) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Fair values of available-for-sale investments by classification in the Consolidated Balance Sheets
Cash and cash equivalents	$ 2,630	$ 4,144	$ 3,795	$ 3,731
Marketable securities	32,404	27,238
Other assets — noncurrent	1,773	1,599
Total available-for-sale investments	34,690	31,112
Available-for-sale investments [Member]
Fair values of available-for-sale investments by classification in the Consolidated Balance Sheets
Cash and cash equivalents	2,163	3,738
Other assets — noncurrent	$ 123	$ 136