Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair value of financial assets and liabilities measured on recurring basis

The following tables 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 December 31, 2017 and 2016.

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 in the following tables on a gross basis. We have no derivative contracts that are subject to master netting arrangements that are reflected gross on the balance sheet.



	December 31, 2017
							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	$	875	$	19	$	—	$	894	$	(893	)	$	—		$	1	$	—
Investments of certain benefit plans	65		—		8		73		n/a			n/a			73		n/a
Total	$	940	$	19	$	8	$	967	$	(893	)	$	—		$	74

Liabilities:
Commodity derivative contracts	$	955	$	14	$	—	$	969	$	(893	)	$	(76	)	$	—	$	(102	)
Environmental credit obligations	—		104		—		104		n/a			n/a			104		n/a
Physical purchase contracts	—		6		—		6		n/a			n/a			6		n/a
Foreign currency contracts	7		—		—		7		n/a			n/a			7		n/a
Total	$	962	$	124	$	—	$	1,086	$	(893	)	$	(76	)	$	117



	December 31, 2016
							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	$	874	$	38	$	—	$	912	$	(875	)	$	—		$	37	$	—
Foreign currency contracts	3		—		—		3		n/a			n/a			3		n/a
Investments of certain benefit plans	58		—		11		69		n/a			n/a			69		n/a
Total	$	935	$	38	$	11	$	984	$	(875	)	$	—		$	109

Liabilities:
Commodity derivative contracts	$	872	$	23	$	—	$	895	$	(875	)	$	(20	)	$	—	$	(88	)
Environmental credit obligations	—		188		—		188		n/a			n/a			188		n/a
Physical purchase contracts	—		5		—		5		n/a			n/a			5		n/a
Total	$	872	$	216	$	—	$	1,088	$	(875	)	$	(20	)	$	193

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 following table along with their associated fair values (in millions):



	December 31, 2017				December 31, 2016
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Financial assets:
Cash and temporary cash investments	$	5,850	$	5,850	$	4,816	$	4,816
Financial liabilities:
Debt (excluding capital leases)	8,310		9,795		7,926		8,882