Fair Value Measurements (Details) (USD $)	6 Months Ended
	Jun. 30, 2012		Dec. 31, 2011
Fair Value Measurements
Net derivative assets	$ 26,000,000		$ 39,000,000
Net derivative liabilities	9,000,000		2,000,000
Total liabilities	15,000,000		5,000,000
Cash collateral posted	21,000,000		75,000,000
Fair value adjustment to physical inventory	0		4,000,000
Percent of trade receivables payables with balances outstanding	1.00%
Days outstanding on trade receivables and payables (days)	90 days
Carrying value of debt	1,700,000,000		1,700,000,000
Fair value of debt	1,800,000,000		1,800,000,000
Commodity Futures Contracts
Fair Value Measurements
Net derivative assets	20,000,000		34,000,000
Net derivative liabilities	9,000,000		0
Commodity OTC Swap Contracts
Fair Value Measurements
Net derivative assets	0		1,000,000
Net derivative liabilities	0		1,000,000
Commodity Forward Contracts
Fair Value Measurements
Net derivative assets	6,000,000		4,000,000
Net derivative liabilities			1,000,000
RINs Obligation
Fair Value Measurements
RINs obligation	6,000,000		3,000,000
Level 1
Fair Value Measurements
Gross derivative assets	588,000,000		86,000,000
Total liabilities	595,000,000		130,000,000
Level 1 | Commodity Futures Contracts
Fair Value Measurements
Gross derivative assets	588,000,000		86,000,000
Gross derivative liabilities	595,000,000		130,000,000
Level 1 | Commodity OTC Swap Contracts
Fair Value Measurements
Gross derivative assets	0		0
Gross derivative liabilities	0		0
Level 1 | Commodity Forward Contracts
Fair Value Measurements
Gross derivative assets	0		0
Gross derivative liabilities			0
Level 1 | RINs Obligation
Fair Value Measurements
RINs obligation	0		0
Level 2
Fair Value Measurements
Gross derivative assets	13,000,000		16,000,000
Total liabilities	16,000,000		13,000,000
Level 2 | Commodity Futures Contracts
Fair Value Measurements
Gross derivative assets	4,000,000		9,000,000
Gross derivative liabilities	7,000,000		6,000,000
Level 2 | Commodity OTC Swap Contracts
Fair Value Measurements
Gross derivative assets	3,000,000		3,000,000
Gross derivative liabilities	3,000,000		3,000,000
Level 2 | Commodity Forward Contracts
Fair Value Measurements
Gross derivative assets	6,000,000		4,000,000
Gross derivative liabilities			1,000,000
Level 2 | RINs Obligation
Fair Value Measurements
RINs obligation	6,000,000		3,000,000
Level 3
Fair Value Measurements
Gross derivative assets	0		0
Total liabilities	0		0
Level 3 | Commodity Futures Contracts
Fair Value Measurements
Gross derivative assets	0		0
Gross derivative liabilities	0		0
Level 3 | Commodity OTC Swap Contracts
Fair Value Measurements
Gross derivative assets	0		0
Gross derivative liabilities	0		0
Level 3 | Commodity Forward Contracts
Fair Value Measurements
Gross derivative assets	0		0
Gross derivative liabilities			0
Level 3 | RINs Obligation
Fair Value Measurements
RINs obligation	0		0
Netting and Collateral (a)
Fair Value Measurements
Net derivative assets	(575,000,000)	[1]	(63,000,000)	[1]
Total liabilities	(596,000,000)	[1]	(138,000,000)	[1]
Netting and Collateral (a) | Commodity Futures Contracts
Fair Value Measurements
Net derivative assets	(572,000,000)	[1]	(61,000,000)	[1]
Net derivative liabilities	(593,000,000)	[1]	(136,000,000)	[1]
Netting and Collateral (a) | Commodity OTC Swap Contracts
Fair Value Measurements
Net derivative assets	(3,000,000)	[1]	(2,000,000)	[1]
Net derivative liabilities	(3,000,000)	[1]	(2,000,000)	[1]
Netting and Collateral (a) | Commodity Forward Contracts
Fair Value Measurements
Net derivative assets	0	[1]	0	[1]
Net derivative liabilities			0	[1]
Netting and Collateral (a) | RINs Obligation
Fair Value Measurements
RINs obligation	$ 0	[1]	$ 0	[1]

[1] Represents the impact of netting assets, liabilities and cash collateral when a legal right of offset exists. As of June 30, 2012 and December 31, 2011, cash collateral amounts of $21 million and $75 million, respectively, are netted with mark-to-market derivative assets.