Delta Air Lines Inc. and Northwest Airline are combining in a stock-swap deal that would create the world’s biggest carrier. The combined airline, which will be called Delta, will have an enterprise value of $17.7 billion, and will be based in Atlanta.

The deal will need antitrust approval, and integrating the work forces of fully unionized Northwest and Delta, where pilots are currently the only major unionized work group, will be tricky.

The joining of Atlanta-based Delta and Eagan, Minn.-based Northwest, if approved by regulators and shareholders of both companies, will result in combined annual revenue of $31.7 billion, vaulting it ahead of Fort Worth, Texas-based AMR Corp.’s American Airlines for the top spot in the U.S.

It would be the biggest carrier in the world in terms of traffic, before any further domestic capacity cuts and any divestitures that might be required by antitrust regulators.