Income taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Current provision
Federal	$ 618	$ 636	$ 325
State	58	52	85
Foreign	148	153	155
Total current provision	824	841	565
Deferred (benefit) provision
Federal	(340)	(196)	92
State	(16)	43	(59)
Foreign	(1)	2	1
Total deferred (benefit) provision	(357)	(151)	34
Total provision	$ 467	$ 690	$ 599