Income taxes - Income tax expense components (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income tax expense:
Federal	$ 3,474	$ 4,546	$ 2,833
State	444	337	124
Foreign	650	724	581
Current	2,897	3,668	1,619
Deferred	1,671	1,939	1,919
Total income taxes	$ 4,568	$ 5,607	$ 3,538