Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 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 balance sheets categorized according to the fair value hierarchy of the inputs utilized by us to determine the fair values as of December 31, 2011 and 2010.

Cash collateral deposits of $136 million and $403 million with brokers under master netting arrangements are included in the fair value of the commodity derivatives reflected in Level 1 as of December 31, 2011 and December 31, 2010, respectively. Certain of our commodity derivative contracts under master netting arrangements include both asset and liability positions. We have elected to offset the fair value amounts recognized for multiple similar derivative instruments executed with the same counterparty, including any related cash collateral asset or obligation under the column “Netting Adjustments” below; however, fair value amounts by hierarchy level are presented on a gross basis in the tables below.

	Fair Value Measurements Using
	Quoted  Prices in Active  Markets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable  Inputs (Level 3)		Netting Adjustments			Total as of December 31, 2011
Assets:
Commodity derivative contracts	$	2,038	$	78		$	—	$	(1,940	)	$	176
Physical purchase contracts	—		(2		)	—		—			(2		)
Investments of certain benefit plans	84		—			11		—			95
Other investments	—		—			—		—			—
Liabilities:
Commodity derivative contracts	1,864		101			—		(1,940		)	25
Obligations of certain benefit plans	34		—			—		—			34

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

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).

	Investments of Certain Benefit Plans						Other Investments								Earn-Out Agreement
	2011		2010		2009		2011			2010			2009		2011		2010		2009
Balance as of beginning of year	$	10	$	10	$	—	$	—		$	—		$	—	$	—	$	—	$	13
Purchases	1		—		—		21			1			—		—		—		—
Settlements	—		—		—		—			—			—		—		—		(33		)
Total losses included in income	—		—		—		(21		)	(1		)	—		—		—		20
Transfers in and/or out of Level 3	—		—		10		—			—			—		—		—		—
Balance as of end of year	$	11	$	10	$	10	$	—		$	—		$	—	$	—	$	—	$	—
The amount of total losses included in income attributable to the change in unrealized losses relating to assets still held at end of period	$	—	$	—	$	—	$	(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):

	December 31,
	2011		2010
Carrying amount	$	7,690	$	8,300
Fair value	9,298		9,492