Contingencies and Commitments (Unaudited) - Tax and Other Matters (Details)	Sep. 30, 2020
PT Freeport Indonesia \| PT Smelting
Loss Contingencies [Line Items]
Investment owned, percent	25.00%

Percent of net assets at close of period. For schedules of investments that are categorized, each category has a percent of net assets for the aggregated value of the Investments in the category.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-12.3)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (b)
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-12C.Column D.2)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010

Name:	us-gaap_InvestmentOwnedPercentOfNetAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant