Income taxes - Income tax expense components (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income tax expense:
Federal	$ 8,155	$ 5,695	$ 3,474
State	258	384	444
Foreign	538	845	650
Current	5,168	4,711	2,897
Deferred	3,783	2,213	1,671
Total income taxes	$ 8,951	$ 6,924	$ 4,568