Schedule of Investments (Unaudited) - Treasury Bills and Money Market Fund - USD ($)		9 Months Ended		12 Months Ended
		Sep. 30, 2017		Dec. 31, 2016
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		98.62%		100.48%
Value		$ 528,403,254		$ 846,158,812
Affiliated Investments, at value		115,167,039		3,786,312
Total Investments in Securities		643,570,293		849,945,124
Investments, cost		$ 643,396,721		849,976,394
Affiliated Investments [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		17.65%
Affiliated Investments, at value		$ 115,167,039
Affiliated Investments, at Cost		$ 115,045,313		$ 3,786,312
U.S. Treasury Bills, 0.970% due October 26, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	2.45%
Value	[1]	$ 15,990,067
Principal Value	[1]	$ 16,000,000
Investment Interest Rate	[1]	0.97%
Investment Maturity Date	[1]	Oct. 26, 2017
U.S. Treasury Bills, 1.020% due December 7, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	18.66%
Value	[1]	$ 121,780,806
Principal Value	[1]	$ 122,000,000
Investment Interest Rate	[1]	1.02%
Investment Maturity Date	[1]	Dec. 07, 2017
U.S. Treasury Bills, 1.050% due January 4, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	35.46%
Value	[1],[2]	$ 231,377,381
Principal Value	[1],[2]	$ 232,000,000
Investment Interest Rate	[1],[2]	1.05%
Investment Maturity Date	[1],[2]	Jan. 04, 2018
Restricted for maintenance margin		$ 19,946,000
U.S. Treasury Bills, 1.115% due March 1, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	24.40%
Value	[1]	$ 159,255,000
Principal Value	[1]	$ 160,000,000
Investment Interest Rate	[1]	1.115%
Investment Maturity Date	[1]	Mar. 01, 2018
United States Treasury Obligations [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		80.97%	[1]	100.03%	[3]
Value		$ 528,403,254	[1]	$ 846,158,812	[3]
Investments, cost		$ 528,351,408	[1]	$ 846,190,082	[3]
Exchange-Traded Fund - PowerShares Treasury Collateral Portfolio [Member] | Affiliated Investments [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[4],[5]	12.28%
Affiliated Investments, at value	[4],[5]	$ 80,128,450
Shares	[4],[5]	757,000
Affiliated Investments, at Cost	[4],[5]	$ 80,006,724
Money Market Mutual Fund - Premier U.S. Government Money Portfolio - Institutional Class [Member] | Affiliated Investments [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		5.37%	[6]	0.45%	[7]
Affiliated Investments, at value		$ 35,038,589	[6]	$ 3,786,312	[7]
Shares		35,038,589	[6]	3,786,312	[7]
Investment Interest Rate		0.92%	[6]	0.41%	[7]
Investments, cost		$ 35,038,589	[6]	$ 3,786,312	[7]
U.S. Treasury Bills, 0.490% due March 2, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3]			4.14%
Value	[3]			$ 34,993,665
Principal Value	[3]			$ 35,000,000
Investment Interest Rate	[3]			0.49%
Investment Maturity Date	[3]			Jan. 19, 2017
U.S. Treasury Bills, 0.485% due January 26, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3]			26.95%
Value	[3]			$ 227,940,036
Principal Value	[3]			$ 228,000,000
Investment Interest Rate	[3]			0.485%
Investment Maturity Date	[3]			Jan. 26, 2017
U.S. Treasury Bills, 0.490% due March 2, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3]			21.26%
Value	[3]			$ 179,862,300
Principal Value	[3]			$ 180,000,000
Investment Interest Rate	[3]			0.49%
Investment Maturity Date	[3]			Mar. 02, 2017
U.S. Treasury Bills, 0.530% due April 6, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[8]			35.53%
Value	[3],[8]			$ 300,594,252
Principal Value	[3],[8]			$ 301,000,000
Investment Interest Rate	[3],[8]			0.53%
Investment Maturity Date	[3],[8]			Apr. 06, 2017
Restricted for maintenance margin				$ 18,973,400
U.S. Treasury Bills, 0.625% due May 18, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3]			12.15%
Value	[3]			$ 102,768,559
Principal Value	[3]			$ 103,000,000
Investment Interest Rate	[3]			0.625%
Investment Maturity Date	[3]			May 18, 2017

[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 $19,946,000 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.

[3] 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 year end.

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

[5] Non-income producing security.

[6] 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, 2017.

[7] 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, 2016.

[8] United States Treasury Obligations of $18,973,400 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.