4. Impairments

The following summarizes impairments by segment:



	Three Months Ended September 30,				Nine Months Ended September 30,
millions	2014		2013		2014		2013
Oil and gas exploration and production
Long-lived assets held for use
U.S. onshore properties	$	387	$	—	$	387	$	—
Gulf of Mexico properties	—		593		115		593
Cost-method investment	—		—		2		10
Midstream
Long-lived assets held for use	7		—		10		29
Total impairments	$	394	$	593	$	514	$	632

In the third quarter of 2014, a U.S. onshore oil and gas property was impaired due to lower forecasted natural-gas prices. In the second quarter of 2014, the Company impaired a Gulf of Mexico property due to a reduction in estimated future cash flows. In the third quarter of 2013, certain Gulf of Mexico properties were impaired due to a reduction in estimated future net cash flows and downward revisions of reserves resulting from changes to the Company’s development plans. In the second quarter of 2013, the Company impaired its Venezuelan cost-method investment due to declines in estimated recoverable value. In addition, during the first quarter of 2013, a midstream property was impaired due to a reduction in estimated future cash flows.

The following summarizes the post-impairment fair value of the above-described assets, which was measured using the income approach and Level 3 inputs:



millions	2014		2013
Long-lived assets held for use	$	661	$	266
Cost-method investment⁽¹⁾	32		32

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⁽¹⁾	This represents the Company’s after-tax net investment.