Additional Financial Information - Summary of the Tiered Valuation Input Levels (Detail) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
United States Treasury Obligations	$ 1,371,935,248	$ 2,403,838,023
Exchange-Traded Fund	250,525,440
Money Market Mutual Fund	96,035,039	131,029,805
Total investments, at value (cost $1,717,876,964 and $2,534,934,371, respectively)	1,718,495,727	2,534,867,828
Commodity Futures Contracts	(100,033,905)	101,032,417
Total Investments	1,618,461,822	2,635,900,245
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exchange-Traded Fund	250,525,440
Money Market Mutual Fund	96,035,039	131,029,805
Total investments, at value (cost $1,717,876,964 and $2,534,934,371, respectively)	346,560,479	131,029,805
Commodity Futures Contracts	(100,033,905)	101,032,417
Total Investments	246,526,574	232,062,222
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
United States Treasury Obligations	1,371,935,248	2,403,838,023
Total investments, at value (cost $1,717,876,964 and $2,534,934,371, respectively)	1,371,935,248	2,403,838,023
Total Investments	$ 1,371,935,248	$ 2,403,838,023