Receivables (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Receivables
Accounts receivable	$ 8,366	$ 4,299
Commodity derivative receivables	174	144
Notes receivable and other	214	182
Receivables, gross	8,754	4,625
Allowance for doubtful accounts	(48)	(42)	(45)
Receivables, net	8,706	4,583
Changes in the allowance for doubtful accounts
Balance as of beginning of year	42	45	58
Increase in allowance charged to expense	21	14	28
Accounts charged against the allowance, net of recoveries	(14)	(17)	(42)
Foreign currency translation	(1)	0	1
Balance as of end of year	$ 48	$ 42	$ 45