Income taxes - Income tax expense components (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income tax expense:
Federal	$ 5,695	$ 3,474	$ 4,546
State	384	444	337
Foreign	845	650	724
Current	4,711	2,897	3,668
Deferred	2,213	1,671	1,939
Total income taxes	$ 6,924	$ 4,568	$ 5,607