Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified																																																								6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Commodity Futures Contracts	Dec. 31, 2013 Commodity Futures Contracts	Jun. 30, 2014 Commodity OTC Swap Contracts	Jun. 30, 2014 Commodity Forward Contracts	Dec. 31, 2013 Commodity Forward Contracts	Jun. 30, 2014 Environmental Credit Obligations	Dec. 31, 2013 Environmental Credit Obligations	Jun. 30, 2014 Level 1	Dec. 31, 2013 Level 1	Jun. 30, 2014 Level 1 Commodity Futures Contracts	Dec. 31, 2013 Level 1 Commodity Futures Contracts	Jun. 30, 2014 Level 1 Commodity OTC Swap Contracts	Jun. 30, 2014 Level 1 Commodity Forward Contracts	Dec. 31, 2013 Level 1 Commodity Forward Contracts	Jun. 30, 2014 Level 1 Environmental Credit Obligations	Dec. 31, 2013 Level 1 Environmental Credit Obligations	Jun. 30, 2014 Level 2	Dec. 31, 2013 Level 2	Jun. 30, 2014 Level 2 Commodity Futures Contracts	Dec. 31, 2013 Level 2 Commodity Futures Contracts	Jun. 30, 2014 Level 2 Commodity OTC Swap Contracts	Jun. 30, 2014 Level 2 Commodity Forward Contracts	Dec. 31, 2013 Level 2 Commodity Forward Contracts	Jun. 30, 2014 Level 2 Environmental Credit Obligations	Dec. 31, 2013 Level 2 Environmental Credit Obligations	Jun. 30, 2014 Level 3	Dec. 31, 2013 Level 3	Jun. 30, 2014 Level 3 Commodity Futures Contracts	Dec. 31, 2013 Level 3 Commodity Futures Contracts	Jun. 30, 2014 Level 3 Commodity OTC Swap Contracts	Jun. 30, 2014 Level 3 Commodity Forward Contracts	Dec. 31, 2013 Level 3 Commodity Forward Contracts	Jun. 30, 2014 Level 3 Environmental Credit Obligations	Dec. 31, 2013 Level 3 Environmental Credit Obligations	Jun. 30, 2014 Netting and Collateral		Dec. 31, 2013 Netting and Collateral		Jun. 30, 2014 Netting and Collateral Commodity Futures Contracts		Dec. 31, 2013 Netting and Collateral Commodity Futures Contracts		Jun. 30, 2014 Netting and Collateral Commodity OTC Swap Contracts		Jun. 30, 2014 Netting and Collateral Commodity Forward Contracts		Dec. 31, 2013 Netting and Collateral Commodity Forward Contracts		Jun. 30, 2014 Netting and Collateral Environmental Credit Obligations		Dec. 31, 2013 Netting and Collateral Environmental Credit Obligations		Jun. 30, 2014 Maximum	Jun. 30, 2014 Minimum
Fair Value Measurements
Gross derivative assets	$ 262	$ 140								$ 252	$ 136	$ 252	$ 136		$ 0				$ 10	$ 4	$ 8	$ 4		$ 2				$ 0	$ 0	$ 0	$ 0		$ 0
Derivative asset amount offset against collateral and netting arrangements																																					(175)	[1]	(72)	[1]	(175)	[1]	(72)	[1]			0	[1]
Net derivative assets	87	68	85	68		2
Gross derivative liabilities	276	159								265	156	265	156	0	0	0	0	0	26	8	7	2	3	1	1	15	5	0	0	0	0	0	0	0	0	0
Derivative liability amount offset against collateral and netting arrangements																																					(249)	[1]	(137)	[1]	(249)	[1]	(137)	[1]	0	[1]	0	[1]	0	[1]	0	[1]	0	[1]
Net derivative liabilities	42	27	23	21	3	1	1	15	5
Cash collateral posted	74	65
Percent of trade receivables with balances outstanding greater than 90 days																																																							1.00%
Percent of trade payables with balances outstanding greater than 90 days																																																							1.00%
Days Outstanding On Acccounts Payable and Receivable																																																								90 days
Debt carrying value, excluding capital lease obligations	3,000
Debt carrying value	3,055	2,823
Debt fair value	$ 3,100	$ 2,900

[1] Represents the impact of netting assets, liabilities and cash collateral when a legal right of offset exists. 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.