Statements of Financial Condition (Unaudited) (Parenthetical) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Investments, cost	$ 539,598,907	$ 849,976,394
US Treasury Bill Securities [Member]
Investments, cost	$ 537,558,967	$ 846,190,082

Cost of the investment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=63488139&loc=d3e12121-115841

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant