Schedule of Investments (Unaudited) - Treasury Bills and Money Market Fund - USD ($)		3 Months Ended		12 Months Ended
		Mar. 31, 2019		Dec. 31, 2018
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity		99.57%		101.65%
United States Treasury Obligations, Value		$ 22,865,913		$ 20,955,757
Affiliated Investments, Value		1,524,446		2,951,903
Investments in Securities, Value		24,390,359		23,907,660
Investments in Securities, Cost		$ 24,388,446		$ 23,906,786
U.S. Treasury Bills, 2.375% due May 2, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	16.30%
United States Treasury Obligations, Value	[1],[2]	$ 3,991,927
United States Treasury Obligations, Principal Value	[1],[2]	$ 4,000,000
Investment Interest Rate	[1],[2]	2.375%
Restricted for maintenance margin		$ 508,929
Investment Maturity Date	[1],[2]	May 02, 2019
U.S. Treasury Bills, 2.470% due July 11, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	77.05%
United States Treasury Obligations, Value	[1]	$ 18,873,986
United States Treasury Obligations, Principal Value	[1]	$ 19,000,000
Investment Interest Rate	[1]	2.47%
Investment Maturity Date	[1]	Jul. 11, 2019
United States Treasury Obligations [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	93.35%		89.10%
United States Treasury Obligations, Value	[1]	$ 22,865,913		$ 20,955,757
Investments in Securities, Cost	[1]	$ 22,864,000		$ 20,954,883
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		6.22%	[3]	12.55%	[4]
Affiliated Investments, Value		$ 1,524,446	[3]	$ 2,951,903	[4]
Affiliated Investments, Shares		1,524,446	[3]	2,951,903	[4]
Affiliated Investments, at Cost		$ 1,524,446	[3]	$ 2,951,903	[4]
Investment Interest Rate		2.33%	[3]	2.30%	[4]
U.S. Treasury Bills, 2.175% due January 3, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			59.52%
United States Treasury Obligations, Value	[1]			$ 13,999,127
United States Treasury Obligations, Principal Value	[1]			$ 14,000,000
Investment Interest Rate	[1]			2.175%
Investment Maturity Date	[1]			Jan. 03, 2019
U.S. Treasury Bills, 2.370% due February 28, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			12.71%
United States Treasury Obligations, Value	[1]			$ 2,988,713
United States Treasury Obligations, Principal Value	[1]			$ 3,000,000
Investment Interest Rate	[1]			2.37%
Investment Maturity Date	[1]			Feb. 28, 2019
U.S. Treasury Bills, 2.430% due May 2, 2019 [Member]
Schedule Of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[5]			16.87%
United States Treasury Obligations, Value	[1],[5]			$ 3,967,917
United States Treasury Obligations, Principal Value	[1],[5]			$ 4,000,000
Investment Interest Rate	[1],[5]			2.43%
Restricted for maintenance margin				$ 505,920
Investment Maturity Date	[1],[5]			May 02, 2019

[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 $508,929 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 March 31, 2019.

[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, 2018.

[5] United States Treasury Obligations of $505,920 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.