Schedule of Investments - Treasury Bills and Money Market Fund - USD ($)		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		95.33%		99.12%
Value		$ 1,839,039,728		$ 2,403,838,023
Affiliated investments, at value		317,746,227		131,029,805
Total Investments in Securities		2,156,785,955		2,534,867,828
Investments, cost		$ 2,157,140,963		2,534,934,371
Affiliated Investments [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		14.04%
Affiliated investments, at value		$ 317,746,227
Affiliated Investments, at Cost		$ 317,993,905		$ 131,029,805
U.S. Treasury Bills, 1.180% due January 4, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	13.30%
Value	[1]	$ 300,981,124
Principal Value	[1]	$ 301,000,000
Investment Interest Rate		1.18%
Investment Maturity Date		Jan. 04, 2018
U.S. Treasury Bills, 1.245% due January 18, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	12.77%
Value	[1]	$ 288,841,533
Principal Value	[1]	$ 289,000,000
Investment Interest Rate		1.245%
Investment Maturity Date		Jan. 18, 2018
U.S. Treasury Bills, 1.285% due February 22, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	26.78%
Value	[1]	$ 605,916,505
Principal Value	[1]	$ 607,000,000
Investment Interest Rate		1.285%
Investment Maturity Date		Feb. 22, 2018
U.S. Treasury Bills, 1.285% due March 1, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	24.53%
Value	[1],[2]	$ 554,864,604
Principal Value	[1],[2]	$ 556,000,000
Investment Interest Rate	[2]	1.285%
Investment Maturity Date	[2]	Mar. 01, 2018
Restricted for maintenance margin		$ 199,580,000
U.S. Treasury Bills, 1.450% due June 7, 2018 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	3.91%
Value	[1]	$ 88,435,962
Principal Value	[1]	$ 89,000,000
Investment Interest Rate		1.45%
Investment Maturity Date		Jun. 07, 2018
United States Treasury Obligations [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		81.29%	[1]	93.99%	[3]
Value		$ 1,839,039,728	[1]	$ 2,403,838,023	[3]
Investments, cost		$ 1,839,147,058		$ 2,403,904,566
Exchange-Traded Fund - PowerShares Treasury Collateral Portfolio [Member] | Affiliated Investments [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[4]	11.04%
Affiliated investments, at value	[4]	$ 249,742,548
Shares	[4]	2,372,400
Affiliated Investments, at Cost		$ 249,990,226
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		3.00%	[5]	5.13%	[6]
Affiliated investments, at value		$ 68,003,679	[5]	$ 131,029,805	[6]
Shares		68,003,679	[5]	131,029,805	[6]
Investment Interest Rate		1.15%		0.41%
Affiliated Investments, at Cost		$ 68,003,679		$ 131,029,805
U.S. Treasury Bills, 0.490% due January 19, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3]			21.89%
Value	[3]			$ 559,898,640
Principal Value	[3]			$ 560,000,000
Investment Interest Rate				0.49%
Investment Maturity Date				Jan. 19, 2017
U.S. Treasury Bills, 0.485% due January 26, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3]			18.61%
Value	[3]			$ 475,874,812
Principal Value	[3]			$ 476,000,000
Investment Interest Rate				0.485%
Investment Maturity Date				Jan. 26, 2017
U.S. Treasury Bills, 0.490% due March 2, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3]			16.41%
Value	[3]			$ 419,678,700
Principal Value	[3]			$ 420,000,000
Investment Interest Rate				0.49%
Investment Maturity Date				Mar. 02, 2017
U.S. Treasury Bills, 0.530% due April 6, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[7]			22.61%
Value	[3],[7]			$ 578,219,508
Principal Value	[3],[7]			$ 579,000,000
Investment Interest Rate	[7]			0.53%
Investment Maturity Date	[7]			Apr. 06, 2017
Restricted for maintenance margin				$ 244,657,000
U.S. Treasury Bills, 0.625% due May 18, 2017 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3]			14.47%
Value	[3]			$ 370,166,363
Principal Value	[3]			$ 371,000,000
Investment Interest Rate				0.625%
Investment Maturity Date				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 $199,580,000 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] 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.

[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 December 31, 2016.

[7] United States Treasury Obligations of $244,657,000 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.