Schedule of Investments (Unaudited) - Treasury Bills and Money Market Fund - USD ($)		9 Months Ended		12 Months Ended
		Sep. 30, 2018		Dec. 31, 2017
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity		100.29%		99.15%
Value		$ 27,856,750		$ 37,933,681
Affiliated investments, at value		2,366,117		2,095,110
Total Investments in Securities		30,222,867		40,028,791
Investments in Securities, cost		$ 30,228,850		$ 40,033,382
U.S. Treasury Bills, 2.010% due November 8, 2018 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	23.18%
Value	[1]	$ 6,984,742
Principal Value	[1]	$ 7,000,000
Investment Interest Rate	[1]	2.01%
Investment Maturity Date	[1]	Nov. 08, 2018
U.S. Treasury Bills, 2.095% due December 6, 2018 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	19.83%
Value	[1]	$ 5,976,653
Principal Value	[1]	$ 6,000,000
Investment Interest Rate	[1]	2.095%
Investment Maturity Date	[1]	Dec. 06, 2018
U.S. Treasury Bills, 2.175% due January 3, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	32.99%
Value	[1],[2]	$ 9,942,751
Principal Value	[1],[2]	$ 10,000,000
Investment Interest Rate	[1],[2]	2.175%
Investment Maturity Date	[1],[2]	Jan. 03, 2019
Restricted for maintenance margin		$ 1,998,543
U.S. Treasury Bills, 2.210% due February 28, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	16.44%
Value	[1]	$ 4,952,604
Principal Value	[1]	$ 5,000,000
Investment Interest Rate	[1]	2.21%
Investment Maturity Date	[1]	Feb. 28, 2019
United States Treasury Obligations [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	92.44%		93.96%
Value	[1]	$ 27,856,750		$ 37,933,681
Investments in Securities, cost	[1]	$ 27,862,733		$ 37,938,272
Money Market Mutual Fund - Invesco Premier U.S. Government Money Portfolio - Institutional Class [Member] | Affiliated Investments [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity		7.85%	[3]	5.19%	[4]
Affiliated investments, at value		$ 2,366,117	[3]	$ 2,095,110	[4]
Shares		2,366,117	[3]	2,095,110	[4]
Investment Interest Rate		1.95%	[3]	1.15%	[4]
Investments in Securities, cost		$ 2,366,117	[3]	$ 2,095,110	[4]
U.S. Treasury Bills, 1.180% due January 4, 2018 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			22.29%
Value	[1]			$ 8,999,436
Principal Value	[1]			$ 9,000,000
Investment Interest Rate	[1]			1.18%
Investment Maturity Date	[1]			Jan. 04, 2018
U.S. Treasury Bills, 1.285% due February 22, 2018 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			19.78%
Value	[1]			$ 7,985,720
Principal Value	[1]			$ 8,000,000
Investment Interest Rate	[1]			1.285%
Investment Maturity Date	[1]			Feb. 22, 2018
U.S. Treasury Bills, 1.285% due March 1, 2018 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[5]			46.97%
Value	[1],[5]			$ 18,961,200
Principal Value	[1],[5]			$ 19,000,000
Investment Interest Rate	[1],[5]			1.285%
Investment Maturity Date	[1],[5]			Mar. 01, 2018
Restricted for maintenance margin				$ 2,993,700
U.S. Treasury Bills, 1.450% due June 7, 2018 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			4.92%
Value	[1]			$ 1,987,325
Principal Value	[1]			$ 2,000,000
Investment Interest Rate	[1]			1.45%
Investment Maturity Date	[1]			Jun. 07, 2018

[1] Security may be traded on a discount basis. The interest rate shown represents the discount rate at the most recent auction date of the security prior to period end.

[2] United States Treasury Obligations of $1,998,543 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.

[3] The security and the Fund are advised by wholly-owned subsidiaries of Invesco Ltd. and are therefore considered to be affiliated. The rate shown is the 7-day SEC standardized yield as of September 30, 2018.

[4] The security and the Fund are advised by wholly-owned subsidiaries of Invesco Ltd. and are therefore considered to be affiliated. The rate shown is the 7-day SEC standardized yield as of December 31, 2017.

[5] United States Treasury Obligations of $2,993,700 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.