Available-for-sale investments (Details 1) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Fair values of available-for-sale investments by classification in the Consolidated Balance Sheets
Cash and cash equivalents	$ 8,281	$ 3,257	$ 5,823	$ 6,946
Marketable securities	14,277	20,804
Other assets — noncurrent	1,450	1,133
Restricted investments	3,411	0
Total available-for-sale investments	25,605	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	7,830	2,887
Other assets — noncurrent	91	54
Restricted investments		0
ATL Holdings [Member] | Available-for-sale investments [Member]
Fair values of available-for-sale investments by classification in the Consolidated Balance Sheets
Restricted investments	$ 3,407