Schedule of Investments - Treasury Bills and Money Market Fund - USD ($)		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		103.49%		101.59%
United States Treasury Obligations, Value		$ 409,384,745		$ 460,172,505
Affiliated Investments, Value		102,216,801		81,011,698
Investments in Securities, Value		511,601,546		541,184,203
Investments in Securities, Cost		511,790,491		$ 541,547,464
Restricted for maintenance margin		$ 10,614,400
Affiliated Investments [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		20.68%		15.21%
Affiliated Investments, Value		$ 102,216,801		$ 81,011,698
Affiliated Investments, at Cost		$ 102,405,445		$ 81,329,032
U.S. Treasury Bills, 2.175% due January 3, 2019 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	24.68%
United States Treasury Obligations, Value	[1]	$ 121,992,392
United States Treasury Obligations, Principal Value	[1]	$ 122,000,000
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]	29.02%
United States Treasury Obligations, Value	[1]	$ 143,458,214
United States Treasury Obligations, Principal Value	[1]	$ 144,000,000
Investment Interest Rate	[1]	2.37%
Investment Maturity Date	[1]	Feb. 28, 2019
U.S. Treasury Bills, 2.465% due April 4, 2019 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	10.65%
United States Treasury Obligations, Value	[1]	$ 52,672,055
United States Treasury Obligations, Principal Value	[1]	$ 53,000,000
Investment Interest Rate	[1]	2.465%
Investment Maturity Date	[1]	Apr. 04, 2019
U.S. Treasury Bills, 2.430% due May 2, 2019 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	18.46%
United States Treasury Obligations, Value	[1],[2]	$ 91,262,084
United States Treasury Obligations, Principal Value	[1],[2]	$ 92,000,000
Investment Interest Rate	[1],[2]	2.43%
Investment Maturity Date	[1],[2]	May 02, 2019
United States Treasury Obligations [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	82.81%		86.38%
United States Treasury Obligations, Value	[1]	$ 409,384,745		$ 460,172,505
Investments in Securities, Cost	[1]	$ 409,385,046		$ 460,218,432
Exchange-Traded Fund [Member] | Affiliated Investments [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		16.15%	[3]	14.96%	[4]
Affiliated Investments, Value		$ 79,818,080	[3]	$ 79,689,390	[4]
Affiliated Investments, Shares		757,000	[3]	757,000	[4]
Affiliated Investments, at Cost		$ 80,006,724	[3]	$ 80,006,724	[4]
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		4.53%	[5]	0.25%	[6]
Affiliated Investments, Value		$ 22,398,721	[5]	$ 1,322,308	[6]
Affiliated Investments, Shares		22,398,721	[5]	1,322,308	[6]
Investment Interest Rate		2.30%	[5]	1.15%	[6]
Investments in Securities, Cost		$ 22,398,721	[5]	$ 1,322,308	[6]
U.S. Treasury Bills, 1.180% due January 4, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			35.10%
United States Treasury Obligations, Value	[1]			$ 186,988,273
United States Treasury Obligations, Principal Value	[1]			$ 187,000,000
Investment Interest Rate	[1]			1.18%
Investment Maturity Date	[1]			Jan. 04, 2018
U.S. Treasury Bills, 1.245% due January 18, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			4.50%
United States Treasury Obligations, Value	[1]			$ 23,986,840
United States Treasury Obligations, Principal Value	[1]			$ 24,000,000
Investment Interest Rate	[1]			1.245%
Investment Maturity Date	[1]			Jan. 18, 2018
U.S. Treasury Bills, 1.285% due March 1, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[7]			34.10%
United States Treasury Obligations, Value	[1],[7]			$ 181,628,342
United States Treasury Obligations, Principal Value	[1],[7]			$ 182,000,000
Investment Interest Rate	[1],[2]			1.285%
Investment Maturity Date	[1],[2]			Mar. 01, 2018
Restricted for maintenance margin				$ 19,958,000
U.S. Treasury Bills, 1.450% due June 7, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]			12.68%
United States Treasury Obligations, Value	[1]			$ 67,569,050
United States Treasury Obligations, Principal Value	[1]			$ 68,000,000
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 $10,614,400 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.

[3] Affiliated company. The security and the Fund are affiliated by having the same investment adviser. See Note 8.

[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] 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.

[6] Unrealized Appreciation (Depreciation) and Value are presented above, net by contract.

[7] United States Treasury Obligations of $19,958,000 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.