Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2011

Fair Value Measurements [Abstract]

Fair value of financial assets and liabilities measured and recorded on recurring basis

The tables below present information (in millions) about our financial instruments recognized at their fair values in our consolidated balance sheets categorized according to the fair value hierarchy of the inputs utilized by us to determine the fair values as of September 30, 2011 and December 31, 2010.

	Fair Value Measurements Using
	Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)					Total as of September 30, 2011
								Netting Adjustments
Assets:
Commodity derivative contracts	$	6,764	$	238		$	—	$	(6,734	)	$	268
Physical purchase contracts	—		(81		)	—		—			(81		)
Investments of nonqualified benefit plans	81		—			11		—			92
Other investments	—		—			—		—			—
Liabilities:
Commodity derivative contracts	6,503		338			—		(6,734		)	107
Nonqualified benefit plan obligations	34		—			—		—			34
RINs obligation	137		—			—		—			137

	Fair Value Measurements Using
	Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)					Total as of December 31, 2010
							Netting Adjustments
Assets:
Commodity derivative contracts	$	3,240	$	489	$	—	$	(3,560	)	$	169
Physical purchase contracts	—		17		—		—			17
Investments of nonqualified benefit plans	104		—		10		—			114
Other investments	—		—		—		—			—
Liabilities:
Commodity derivative contracts	3,097		502		—		(3,560		)	39
Nonqualified benefit plan obligations	36		—		—		—			36
RINs obligation	51		—		—		—			51

Reconciliation of the beginning and ending balances for fair value measurements developed using significant unobservable inputs

The following is a reconciliation of the beginning and ending balances (in millions) for fair value measurements developed using significant unobservable inputs (Level 3).

	2011					2010
	Investments of Nonqualified Benefit Plans		Other Investments			Investments of Nonqualified Benefit Plans		Other Investments
Three months ended September 30:
Balance at beginning of period	$	11	$	—		$	10	$	—
Purchases	—		5			—		—
Total losses included in earnings	—		(5		)	—		—
Transfers in and/or out of Level 3	—		—			—		—
Balance at end of period	$	11	$	—		$	10	$	—
The amount of total losses included   in earnings attributable to the change in   unrealized losses relating to assets still   held at end of period	$	—	$	(5	)	$	—	$	—
Nine months ended September 30:
Balance at beginning of period	$	10	$	—		$	10	$	—
Purchases	—		21			—		1
Total gains (losses) included in   earnings	1		(21		)	—		(1		)
Transfers in and/or out of Level 3	—		—			—		—
Balance at end of period	$	11	$	—		$	10	$	—
The amount of total gains (losses)   included in earnings attributable to the   change in unrealized gains (losses)   relating to assets still held   at end of period	$	1	$	(21	)	$	—	$	(1	)

Estimated fair value of debt including current portion

The fair values of these financial instruments approximate their carrying amounts, except for debt as shown in the table below (in millions):

	September 30, 2011		December 31, 2010
Carrying amount (excluding capital leases)	$	7,595	$	8,300
Fair value	9,169		9,492