Available-for-sale investments (Fair Values by Classification) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Fair values of available-for-sale investments by classification in the Consolidated Balance Sheets
Cash and cash equivalents	$ 3,485	$ 4,144	$ 3,226	$ 3,731
Marketable securities	34,495	27,238
Other assets — noncurrent	1,902	1,599
Total available-for-sale investments	37,728	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	3,070	3,738
Marketable securities	34,495	27,238
Other assets — noncurrent	163	136
Total available-for-sale investments	$ 37,728	$ 31,112