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Mineral Leaseholds, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Summary of minerals leaseholds, net of accumulated depletion [Abstract]
Mineral leaseholds	$ 2,005		$ 1,996
Less accumulated depletion	(399)		(389)
Mineral leaseholds, net	1,606		$ 1,607
Depletion expense related to mineral leaseholds	$ 9	$ 10

X

- Definition

The noncash expense charged against earnings to recognize the consumption of natural resources.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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X

- Definition

The accumulated decrease in the carrying value of the mineral properties as a result of mine or mineral production.

+ References

No definition available.

+ Details

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X

- Definition

Carrying amount at the balance sheet date of mineral properties, gross of adjustments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 360
-Section 25
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=56951519&loc=d3e64895-109465

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e61797-109447

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

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X

- Definition

Mineral properties, net of adjustments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 360
-Section 25
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=56951519&loc=d3e64895-109465

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

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- References

No definition available.

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