Schedules of Investments (Unaudited) - Investments (Details) (Parentheticals) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Cost of short-term investments	$ 431,339,896	$ 720,991,393
Liabilities percentage of net asset value	2.04%	3.20%
Total percentage of net asset value	100.00%	100.00%
United States Treasury Bills 1.57% Due 04/07/20 [Member]
U.S. Treasury bills, effective rate	1.57%
U.S. Treasury bills, due date	Apr. 07, 2020
United States Treasury Bills 1.56% Due 01/07/20 [Member]
U.S. Treasury bills, effective rate		1.56%
U.S. Treasury bills, due date		Jan. 07, 2020
United States Treasury Bills 0.31%-1.55% Due 04/16/20 [Member]
U.S. Treasury bills, due date	Apr. 16, 2020
United States Treasury Bills 0.31%-1.55% Due 04/16/20 [Member] | Minimum [Member]
U.S. Treasury bills, effective rate	0.31%
United States Treasury Bills 0.31%-1.55% Due 04/16/20 [Member] | Maximum [Member]
U.S. Treasury bills, effective rate	1.55%
United States Treasury Bills 1.54% - 1.87% Due 01/16/20 [Member]
U.S. Treasury bills, due date		Jan. 16, 2020
United States Treasury Bills 1.54% - 1.87% Due 01/16/20 [Member] | Minimum [Member]
U.S. Treasury bills, effective rate		1.54%
United States Treasury Bills 1.54% - 1.87% Due 01/16/20 [Member] | Maximum [Member]
U.S. Treasury bills, effective rate		1.87%
United States Treasury Bills 1.55% - 1.61% Due 04/23/20 [Member]
U.S. Treasury bills, due date	Apr. 23, 2020	Apr. 23, 2020
United States Treasury Bills 1.55% - 1.61% Due 04/23/20 [Member] | Minimum [Member]
U.S. Treasury bills, effective rate	1.55%	1.55%
United States Treasury Bills 1.55% - 1.61% Due 04/23/20 [Member] | Maximum [Member]
U.S. Treasury bills, effective rate	1.61%	1.61%
United States Treasury Bills 1.62% Due 01/21/20 [Member]
U.S. Treasury bills, effective rate		1.62%
U.S. Treasury bills, due date		Jan. 21, 2020
United States Treasury Bills 1.87% due 01/23/20 [Member]
U.S. Treasury bills, effective rate		1.87%
U.S. Treasury bills, due date		Jan. 23, 2020
United States Treasury Bills 1.51% - 1.54% Due 05/07/20 [Member]
U.S. Treasury bills, due date	May 07, 2020
United States Treasury Bills 1.51% - 1.54% Due 05/07/20 [Member] | Minimum [Member]
U.S. Treasury bills, effective rate	1.51%
United States Treasury Bills 1.51% - 1.54% Due 05/07/20 [Member] | Maximum [Member]
U.S. Treasury bills, effective rate	1.54%
United States Treasury Bills 1.55% Due 01/30/20 [Member]
U.S. Treasury bills, effective rate		1.55%
U.S. Treasury bills, due date		Jan. 30, 2020
United States Treasury Bills 1.55% - 1.57% Due 05/14/20 [Member]
U.S. Treasury bills, due date	May 14, 2020
United States Treasury Bills 1.55% - 1.57% Due 05/14/20 [Member] | Minimum [Member]
U.S. Treasury bills, effective rate	1.55%
United States Treasury Bills 1.55% - 1.57% Due 05/14/20 [Member] | Maximum [Member]
U.S. Treasury bills, effective rate	1.57%
United States Treasury Bills 1.56% Due 02/04/20 [Member]
U.S. Treasury bills, effective rate		1.56%
U.S. Treasury bills, due date		Feb. 04, 2020
United States Treasury Bills 0.47% - 1.55% Due 05/21/20 [Member]
U.S. Treasury bills, due date	May 21, 2020
United States Treasury Bills 0.47% - 1.55% Due 05/21/20 [Member] | Minimum [Member]
U.S. Treasury bills, effective rate	0.47%
United States Treasury Bills 0.47% - 1.55% Due 05/21/20 [Member] | Maximum [Member]
U.S. Treasury bills, effective rate	1.55%
United States Treasury Bills 1.88% – 1.93% due 02/06/20 [Member]
U.S. Treasury bills, due date		Feb. 06, 2020
United States Treasury Bills 1.88% – 1.93% due 02/06/20 [Member] | Minimum [Member]
U.S. Treasury bills, effective rate		1.88%
United States Treasury Bills 1.88% – 1.93% due 02/06/20 [Member] | Maximum [Member]
U.S. Treasury bills, effective rate		1.93%
United States Treasury Bills 1.52% Due 06/11/20 [Member]
U.S. Treasury bills, effective rate	1.52%
U.S. Treasury bills, due date	Jun. 11, 2020
United States Treasury Bills 1.55% Due 02/13/20 [Member]
U.S. Treasury bills, effective rate		1.55%
U.S. Treasury bills, due date		Feb. 13, 2020
United States Treasury Bills 1.13% Due 06/25/20 [Member]
U.S. Treasury bills, effective rate	1.13%
U.S. Treasury bills, due date	Jun. 25, 2020
United States Treasury Bills 1.55% Due 02/20/20 [Member]
U.S. Treasury bills, effective rate		1.55%
U.S. Treasury bills, due date		Feb. 20, 2020
United States Treasury Bills 1.54% Due 07/02/20 [Member]
U.S. Treasury bills, effective rate	1.54%
U.S. Treasury bills, due date	Jul. 02, 2020
United States Treasury Bills 1.81% Due 02/27/20 [Member]
U.S. Treasury bills, effective rate		1.81%
U.S. Treasury bills, due date		Feb. 27, 2020
United States Treasury Bills 1.06% Due 08/06/20 [Member]
U.S. Treasury bills, effective rate	1.06%
U.S. Treasury bills, due date	Aug. 06, 2020
United States Treasury Bills 1.53% - 1.61% Due 03/12/20 [Member]
U.S. Treasury bills, due date		Mar. 12, 2020
United States Treasury Bills 1.53% - 1.61% Due 03/12/20 [Member] | Minimum [Member]
U.S. Treasury bills, effective rate		1.53%
United States Treasury Bills 1.53% - 1.61% Due 03/12/20 [Member] | Maximum [Member]
U.S. Treasury bills, effective rate		1.61%
US Treasury Bill Securities [Member]
Cost of short-term investments	$ 490,592,111	$ 750,419,242
Percentage of net asset value	97.96%	96.80%
United States Treasury Bills 1.55% Due 03/26/20 [Member]
U.S. Treasury bills, effective rate		1.55%
U.S. Treasury bills, due date		Mar. 26, 2020
United States Treasury Bills 1.55% Due 04/16/20 [Member]
U.S. Treasury bills, effective rate		1.55%
U.S. Treasury bills, due date		Apr. 16, 2020
United States Treasury Bills 1.51% Due 05/07/20 [Member]
U.S. Treasury bills, effective rate		1.51%
U.S. Treasury bills, due date		May 07, 2020
United States Treasury Bills 1.55% due 05/14/20 [Member]
U.S. Treasury bills, effective rate		1.55%
U.S. Treasury bills, due date		May 14, 2020