4. Impairments

The following summarizes impairments by segment:



	Three Months Ended September 30,				Nine Months Ended September 30,
millions	2013		2012		2013		2012
Oil and gas exploration and production
Long-lived assets held for use
U.S. onshore properties	$	—	$	2	$	—	$	81
Gulf of Mexico properties	593		—		593		67
Cost-method investment	—		1		10		12
Midstream
Long-lived assets held for use	—		1		29		6
Impairments	$	593	$	4	$	632	$	166

During the third quarter of 2013, certain Gulf of Mexico properties were impaired due to a reduction in estimated future net cash flows per barrel and downward revisions of reserves that the Company no longer plans to develop. The Company impaired its Venezuelan cost-method investment in 2013 and 2012 due to declines in estimated recoverable value. In addition, a midstream property was impaired during 2013 due to a reduction in estimated future cash flows. In 2012, certain U.S. onshore and midstream properties were impaired primarily due to lower natural-gas prices and a Gulf of Mexico property was impaired as a result of downward reserves revisions for a property that was near the end of its economic life.

The following summarizes the post-impairment fair value of the above-described assets, by asset category and input level within the fair-value hierarchy:



millions
2013	Level 1		Level 2		Level 3⁽¹⁾		Total
Long-lived assets held for use	$	—	$	—	$	266	$	266
Cost-method investment⁽²⁾	—		—		32		32
2012
Long-lived assets held for use	$	—	$	—	$	38	$	38
Cost-method investment⁽²⁾	—		—		34		34

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⁽¹⁾	The income approach was used to measure fair value.


⁽²⁾	This represents the Company’s after-tax net investment.