Fair Value (Tables)

6 Months Ended

Jun. 30, 2013

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis

The following two tables summarize the fair value measurements of our (i) energy commodity derivative contracts; and (ii) interest rate swap agreements as of June 30, 2013 and December 31, 2012, based on the three levels established by the Codification. The fair values of our current and non-current asset and liability derivative contracts are each reported separately as “Fair value of derivative contracts” in the respective sections of our accompanying consolidated balance sheets. The fair value measurements in the tables below do not include cash margin deposits made by us, which are reported within “Other current assets” in our accompanying consolidated balance sheets (in millions).

	Asset fair value measurements using
	Total		Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
As of June 30, 2013
Energy commodity derivative contracts(a)	$	138	$	14	$	89	$	35
Interest rate swap agreements	$	261	$	—	$	261	$	—
As of December 31, 2012
Energy commodity derivative contracts(a)	$	86	$	3	$	76	$	7
Interest rate swap agreements	$	603	$	—	$	603	$	—

	Liability fair value measurements using
	Total			Quoted prices in active markets for identical liabilities (Level 1)			Significant other observable inputs (Level 2)			Significant unobservable inputs (Level 3)
As of June 30, 2013
Energy commodity derivative contracts(a)	$	(39	)	$	(4	)	$	(18	)	$	(17	)
Interest rate swap agreements	$	(49	)	$	—		$	(49	)	$	—
As of December 31, 2012
Energy commodity derivative contracts(a)	$	(33	)	$	(3	)	$	(26	)	$	(4	)
Interest rate swap agreements	$	(1	)	$	—		$	(1	)	$	—

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(a) Level 1 consists primarily of NYMEX natural gas futures. Level 2 consists primarily of OTC WTI swaps and OTC natural gas swaps that are settled on NYMEX. Level 3 consists primarily of WTI options, WTI basis swaps and natural gas liquids options.

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation

The table below provides a summary of changes in the fair value of our Level 3 energy commodity derivative contracts for each of the three and six months ended June 30, 2013 and 2012 (in millions):

Significant unobservable inputs (Level 3)
	Three Months Ended June 30,						Six Months Ended June 30,
	2013			2012			2013			2012
Derivatives-net asset (liability)
Beginning of Period	$	3		$	(3	)	$	3		$	7
Total gains or (losses):
Included in earnings	—			(2		)	6			—
Included in other comprehensive income	1			28			—			6
Purchases(a)	18			—			18			3
Settlements	(4		)	(3		)	(9		)	4
End of Period	$	18		$	20		$	18		$	20
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or (losses) relating to assets held at the reporting date	$	1		$	(2	)	$	5		$	(1	)

Fair Value, by Balance Sheet Grouping

The estimated fair value of our outstanding debt balance as of June 30, 2013 and December 31, 2012 (both short-term and long-term and including debt fair value adjustments), is disclosed below (in millions):

	June 30, 2013				December 31, 2012
	Carrying Value		Estimated Fair value		Carrying Value		Estimated Fair value
Total debt	$	20,654	$	21,240	$	18,760	$	20,439