Schedule of Investments (Unaudited) - Treasury Bills - USD ($)		Jun. 30, 2016		Dec. 31, 2015
Schedule of Investments [Line Items]
Fair Value		$ 2,384,228,085		$ 1,936,908,405
U.S. Treasury Bills, 0.190% due July 7, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	9.79%
Fair Value	[1]	$ 252,997,976
Face Value	[1]	$ 253,000,000
U.S. Treasury Bills, 0.250% due July 21, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	17.41%
Fair Value	[1]	$ 449,956,350
Face Value	[1]	$ 450,000,000
U.S. Treasury Bills, 0.260% due July 28, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	8.51%
Fair Value	[1]	$ 219,971,620
Face Value	[1]	$ 220,000,000
U.S. Treasury Bills, 0.275% due August 4, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	12.73%
Fair Value	[1]	$ 328,934,858
Face Value	[1]	$ 329,000,000
U.S. Treasury Bills, 0.340% due September 1, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	18.30%
Fair Value	[1]	$ 472,818,841
Face Value	[1]	$ 473,000,000
U.S. Treasury Bills, 0.270% due October 6, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1],[2]	13.92%
Fair Value	[1],[2]	$ 359,758,440
Face Value	[1],[2]	$ 360,000,000
U.S. Treasury Bills, 0.400% due October 27, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[1]	11.60%
Fair Value	[1]	$ 299,790,000
Face Value	[1]	$ 300,000,000
United States Treasury Obligations [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity		92.26%	[1]	97.47%	[3],[4]
Fair Value		$ 2,384,228,085	[1]	$ 1,936,908,405	[3],[4]
U.S. Treasury Bills, 0.235% due January 7, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[4]			15.60%
Fair Value	[3],[4]			$ 309,998,760
Face Value	[3],[4]			$ 310,000,000
U.S. Treasury Bills, 0.205% due January 14, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[4]			23.37%
Fair Value	[3],[4]			$ 464,486,994
Face Value	[3],[4]			$ 464,500,000
U.S. Treasury Bills, 0.195% due January 21, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[4]			25.16%
Fair Value	[3],[4]			$ 499,979,500
Face Value	[3],[4]			$ 500,000,000
U.S. Treasury Bills, 0.170% due January 28, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[4]			19.60%
Fair Value	[3],[4]			$ 389,468,061
Face Value	[3],[4]			$ 389,500,000
U.S. Treasury Bills, 0.200% due February 4, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[4]			5.44%
Fair Value	[3],[4]			$ 107,991,576
Face Value	[3],[4]			$ 108,000,000
U.S. Treasury Bills, 0.135% due February 11, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[4]			0.15%
Fair Value	[3],[4]			$ 2,999,604
Face Value	[3],[4]			$ 3,000,000
U.S. Treasury Bills, 0.140% due February 25, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[4]			8.05%
Fair Value	[3],[4]			$ 159,984,320
Face Value	[3],[4]			$ 160,000,000
U.S. Treasury Bills, 0.280% due March 10, 2016 [Member]
Schedule of Investments [Line Items]
Percentage of Shareholders' Equity	[3],[4]			0.10%
Fair Value	[3],[4]			$ 1,999,590
Face Value	[3],[4]			$ 2,000,000

[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 $264,814,500 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] United States Treasury Obligations of $399,960,000 are on deposit with the Commodity Broker and held as maintenance margin for open futures contracts.