The investment seeks to track the investment results of S&P AMT-Free Municipal Series Dec 2024 IndexTM. The fund generally will invest at least 90% of its assets in the component securities of the underlying index. The index measures the performance of investment-grade (as determined by the index provider), tax-exempt U.S. municipal bonds maturing in 2024. It 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.