Impairments

Impairments of Oil and Natural Gas Properties

Our proved oil and natural gas properties are subject to quarterly full cost ceiling tests. Under the ceiling test, capitalized costs, less accumulated amortization and related deferred income taxes, may not exceed an amount equal to the sum of the present value of estimated future net revenues (adjusted for cash flow hedges) less estimated future expenditures to be incurred in developing and producing the proved reserves, less any related income tax effects. Estimated future net revenues for the quarterly ceiling limit are calculated using the average of commodity prices on the first day of the month over the trailing 12-month period. In the Prior Quarter and the Prior Period, capitalized costs of oil and natural gas properties exceeded the ceiling, resulting in an impairment in the carrying value of our oil and natural gas properties of $497 million and $2.564 billion, respectively.

Impairments of Fixed Assets and Other

We review our long-lived assets, other than oil and natural gas properties, for recoverability whenever events or changes in circumstances indicate that carrying amounts may not be recoverable. We recognize an impairment if the carrying amount of a long-lived asset is not recoverable and exceeds its fair value. A summary of our impairments of fixed assets by asset class and other charges for the Current Quarter, the Prior Quarter, the Current Period and the Prior Period is as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
	($ in millions)
Barnett Shale exit costs	$	—	$	616	$	—	$	616
Gathering systems	—		96		—		96
Natural gas compressors	—		32		—		52
Buildings and land	1		7		3		14
Other	8		—		423		17
Total impairments of fixed assets and other	$	9	$	751	$	426	$	795

Barnett Shale Exit Costs. In October 2016, we conveyed our interests in the Barnett Shale operating area located in north central Texas and simultaneously terminated most of our future commitments associated with this asset. As a result of this transaction, we accrued $334 million of charges in the Prior Quarter related to the termination of a natural gas gathering agreement associated with the Barnett Shale assets. We recognized an impairment charge of $282 million in the Prior Quarter related to these assets representing the difference between the carrying amount and the fair value of the assets, less the anticipated costs to sell.

Gathering Systems, Natural Gas Compressors, Buildings and Land. In the Prior Quarter we entered into a purchase and sale agreement to sell the majority of our upstream and midstream assets in the Devonian Shale located in West Virginia and Kentucky. We recognized an impairment charge of $134 million in the Prior Quarter for these assets for the difference between the carrying amount and the fair value of the assets, less the anticipated costs to sell.

Other. In the Current Period, we terminated future natural gas transportation commitments related to divested assets for cash payments of $126 million. In the Current Period, we also paid $290 million to assign an oil transportation agreement to a third party.

Nonrecurring Fair Value Measurements. Fair value measurements for certain of the impairments were based on recent sales information for comparable assets. As the fair value was estimated using the market approach based on recent prices from orderly sales transactions for comparable assets between market participants, these values were classified as Level 2 in the fair value hierarchy. Other inputs used were not observable in the market; these values were classified as Level 3 in the fair value hierarchy.