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FAIR VALUE OF FINANCIAL INSTRUMENTS (Valuation of Securities Using Fair Value Hierarchy) (Detail) - USD ($)
Dec. 31, 2017
Dec. 31, 2016
Short-Term Investments [Member]    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value $ 1,989,077,878 $ 2,770,212,015
Exchange-Traded Futures Contracts [Member] | U S    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value 117,780,350 111,290,560
Fair Value, Inputs, Level 1 [Member] | Short-Term Investments [Member]    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value 1,989,077,878 2,770,212,015
Fair Value, Inputs, Level 1 [Member] | Exchange-Traded Futures Contracts [Member] | U S    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value 117,780,350 111,290,560
Fair Value, Inputs, Level 2 [Member] | Short-Term Investments [Member]    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value 0 0
Fair Value, Inputs, Level 2 [Member] | Exchange-Traded Futures Contracts [Member] | U S    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value 0 0
Fair Value, Inputs, Level 3 [Member] | Short-Term Investments [Member]    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value 0 0
Fair Value, Inputs, Level 3 [Member] | Exchange-Traded Futures Contracts [Member] | U S    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Securities, fair value $ 0 $ 0