Note 3 - Offering of the Shares	3 Months Ended
Mar. 31, 2020
Notes to Financial Statements
Stockholders' Equity Note Disclosure [Text Block]	3 - Offering of the Shares Shares are issued and redeemed continuously in one or more blocks of 50,000 Shares (the “Baskets”) in exchange for Index Futures and cash (or, in the discretion of the Sponsor, other Collateral Assets in lieu of cash). Only registered broker-dealers who have entered into an authorized participant agreement with the Trust (each, an “Authorized Participant”) may purchase or redeem Baskets. Individual investors that are not Authorized Participants cannot purchase or redeem Shares in direct transactions with the Trust. Authorized Participants may redeem their Shares (as well as Shares on behalf of other investors) at any time before 2:40 p.m. (New York time) on any business day in one or more Baskets. Redemptions of Shares in exchange for baskets of Index Futures and cash (or, in the discretion of the Sponsor, other Collateral Assets in lieu of cash) are treated as sales for financial statement purposes. It is possible that, from time to time, BlackRock and/or funds or other accounts managed by the Trustee or an affiliate (collectively, “Affiliates”) may purchase and hold Shares of the Trust. Affiliates reserve the right, subject to compliance with applicable law, to sell into the market or redeem Baskets through an Authorized Participant at any time some or all of the Shares of the Trust acquired for their own accounts. A large sale or redemption of Shares of the Trust by Affiliates could significantly reduce the asset size of the Trust, which might have an adverse effect on the Trust and the Shares that remain outstanding.

Note 3 - Offering of the Shares

3 Months Ended

Mar. 31, 2020

Stockholders' Equity Note Disclosure [Text Block]

3 - Offering of the Shares

Shares are issued and redeemed continuously in one or more blocks of 50,000 Shares (the “Baskets”) in exchange for Index Futures and cash (or, in the discretion of the Sponsor, other Collateral Assets in lieu of cash). Only registered broker-dealers who have entered into an authorized participant agreement with the Trust (each, an “Authorized Participant”) may purchase or redeem Baskets. Individual investors that are not Authorized Participants cannot purchase or redeem Shares in direct transactions with the Trust. Authorized Participants may redeem their Shares (as well as Shares on behalf of other investors) at any time before 2:40 p.m. (New York time) on any business day in one or more Baskets. Redemptions of Shares in exchange for baskets of Index Futures and cash (or, in the discretion of the Sponsor, other Collateral Assets in lieu of cash) are treated as sales for financial statement purposes.

It is possible that, from time to time, BlackRock and/or funds or other accounts managed by the Trustee or an affiliate (collectively, “Affiliates”) may purchase and hold Shares of the Trust. Affiliates reserve the right, subject to compliance with applicable law, to sell into the market or redeem Baskets through an Authorized Participant at any time some or all of the Shares of the Trust acquired for their own accounts. A large sale or redemption of Shares of the Trust by Affiliates could significantly reduce the asset size of the Trust, which might have an adverse effect on the Trust and the Shares that remain outstanding.