Derivative Instruments, Derivative Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Derivatives, Fair Value
Gross derivative assets	$ 262		$ 140
Gross derivative liabilities	276		159
Net derivative assets	87		68
Net derivative liabilities	27		22
Derivative, Collateral
Cash collateral outstanding	74		65
Commodity Futures Contracts | Prepayments and other current assets
Derivatives, Fair Value
Gross derivative assets	260	[1]	140	[1]
Gross derivative liabilities	272	[1]	158	[1]
Commodity OTC Swap Contracts | Accounts payable
Derivatives, Fair Value
Gross derivative assets	0		0
Gross derivative liabilities	3		0
Commodity Forward Contracts | Accounts payable
Derivatives, Fair Value
Gross derivative assets	0		0
Gross derivative liabilities	1		1
Commodity Forward Contracts | Receivables
Derivatives, Fair Value
Gross derivative assets	2		0
Gross derivative liabilities	0		0
Counterparty Netting and Cash Collateral
Derivatives, Fair Value
Derivative asset amount offset against collateral and netting arrangements	(175)	[2]	(72)	[2]
Derivative liability amount offset against collateral and netting arrangements	(249)	[2]	(137)	[2]
Commodity Contract, Corn Futures
Derivatives, Fair Value
Gross derivative assets	13		3
Gross derivative liabilities	$ 10		$ 1

[1] We had derivative assets totaling $13 million and $3 million at June 30, 2014 and December 31, 2013, respectively, related to corn futures used to manage our biofuel exposure. Additionally, we had derivative liabilities totaling $10 million and $1 million at June 30, 2014 and December 31, 2013, respectively, related to corn futures.

[2] As of June 30, 2014 and December 31, 2013, cash collateral amounts of $74 million and $65 million, respectively, are netted with mark-to-market derivative assets.