Reuters S&P Global has struck a deal to buy IHS Markit for $44 billion, the companies announced Monday.The mega deal marks the largest transaction on Wall Street this year, according to Dealogic.Upon completion of the deal, current S&P Global shareholders will own about 68% of the combined company on a fully diluted basis, while IHS Markit shareholders will own about 32%.The deal is expected to close in the second half of 2021.The combined group expects to generate annual free cash flow exceeding $5 billion by 2023.Visit Business Insider's homepage for more stories.S&P Global has agreed to buy IHS Markit for $44 billion in an all-stock deal that brings together two powerful Wall Street financial data services, the companies announced Monday.The merger challenges two of the largest global data providers, Bloomberg and Refinitiv.