Statements of Financial Condition (Unaudited) (Parenthetical) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Investments, cost	$ 2,194,930,838	$ 2,534,934,371
US Treasury Bill Securities [Member]
Investments, cost	1,849,014,340	2,403,904,566
Affiliated Investments [Member]
Affiliated Investments, at Cost	$ 345,916,498	$ 131,029,805