Statements of Financial Condition (Unaudited) (Parenthetical) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Investments in Securities, cost	$ 1,766,964,593	$ 2,009,415,674
US Treasury Bill Securities [Member]
Investments in Securities, cost	1,447,642,314	1,614,486,381
Affiliated Investments [Member]
Affiliated Investments, at Cost	$ 319,322,279	$ 394,929,293