Statements of Financial Condition (Unaudited) (Parenthetical) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Investments in Securities, cost	$ 3,007,090,921	$ 2,157,140,963
US Treasury Bill Securities [Member]
Investments in Securities, cost	2,608,928,624	1,839,147,058
Affiliated Investments [Member]
Affiliated Investments, at Cost	$ 398,162,297	$ 317,993,905