Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2015

Fair Value Disclosures [Abstract]

Fair value of assets and liabilities measured on recurring basis

The tables below present information (in millions) about our assets and liabilities 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 March 31, 2015 and December 31, 2014.

We have elected to offset the fair value amounts recognized for multiple similar derivative contracts executed with the same counterparty, including any related cash collateral assets or obligations as shown below; however, fair value amounts by hierarchy level are presented on a gross basis in the tables below. We have no derivative contracts that are subject to master netting arrangements that are reflected gross on the balance sheet.

	March 31, 2015
							Total Gross Fair Value		Effect of Counter- party Netting			Effect of Cash Collateral Netting			Net Carrying Value on Balance Sheet		Cash Collateral Paid or Received Not Offset
	Fair Value Hierarchy
	Level 1		Level 2		Level 3
Assets:
Commodity derivative contracts	$	2,438	$	30	$	—	$	2,468	$	(2,443	)	$	—		$	25	$	—
Foreign currency contracts	3		—		—		3		n/a			n/a			3		n/a
Investments of certain benefit plans	91		—		11		102		n/a			n/a			102		n/a
Total	$	2,532	$	30	$	11	$	2,573	$	(2,443	)	$	—		$	130
Liabilities:
Commodity derivative contracts	$	2,455	$	34	$	—	$	2,489	$	(2,443	)	$	(46	)	$	—	$	(155	)
Environmental credit obligations	—		43		—		43		n/a			n/a			43		n/a
Physical purchase contracts	—		4		—		4		n/a			n/a			4		n/a
Total	$	2,455	$	81	$	—	$	2,536	$	(2,443	)	$	(46	)	$	47

	December 31, 2014
							Total Gross Fair Value		Effect of Counter- party Netting			Effect of Cash Collateral Netting			Net Carrying Value on Balance Sheet		Cash Collateral Paid or Received Not Offset
	Fair Value Hierarchy
	Level 1		Level 2		Level 3
Assets:
Commodity derivative contracts	$	3,096	$	36	$	—	$	3,132	$	(2,907	)	$	(99	)	$	126	$	—
Physical purchase contracts	—		1		—		1		n/a			n/a			1		n/a
Investments of certain benefit plans	97		—		11		108		n/a			n/a			108		n/a
Total	$	3,193	$	37	$	11	$	3,241	$	(2,907	)	$	(99	)	$	235
Liabilities:
Commodity derivative contracts	$	2,886	$	34	$	—	$	2,920	$	(2,907	)	$	(13	)	$	—	$	(25	)
Environmental credit obligations	—		14		—		14		n/a			n/a			14		n/a
Physical purchase contracts	—		5		—		5		n/a			n/a			5		n/a
Total	$	2,886	$	53	$	—	$	2,939	$	(2,907	)	$	(13	)	$	19

Carrying amounts and estimated fair value of financial instruments

Financial instruments that we recognize in our balance sheets at their carrying amounts are shown in the table below (in millions):

	March 31, 2015				December 31, 2014
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Financial assets:
Cash and temporary cash investments	$	4,870	$	4,870	$	3,689	$	3,689
Financial liabilities:
Debt (excluding capital leases)	7,393		8,798		6,354		7,562