The investment seeks to track the investment results of the S&P AMT-Free Municipal Series Dec 2023 IndexTM composed of investment-grade U.S. municipal bonds maturing after December 31, 2022 and before December 2, 2023. The fund generally will invest at least 90% of its assets in the component securities of the index, and may invest up to 10% of its assets in certain futures, options and swap contracts, cash and cash equivalents. The index includes municipal bonds primarily from issuers that are state or local governments or agencies such that the interest on the bonds is exempt from U.S. federal income taxes.