Reuters was first to report on Monday that private equity firm GTCR LLC was in advanced talks to acquire a majority stake in the merchant business of payment processing company Fidelity National Information Services in a deal that values the division at between $15 billion and $20 billion. The deal would be the largest in GTCR’s history and would enable FIS to undo its $43 billion acquisition of WorldPay, which it completed four years ago. WorldPay now comprises the bulk of the FIS merchant business. The deal was announced today, confirming Reuters reporting.