If Delta and Northwest are going to complete their deal to create the world's largest airline, they have some roadblocks to overcome first. Two of Northwest's largest unions immediately declared their opposition.

Most importantly, the airlines will need antitrust approval from federal regulators. In 2001, an attempted merger of United Airlines and US Airways fell apart amid antitrust concerns. Executives at Delta and Northwest said they are aiming to close their deal by the end of this year, which would be before the end of the merger-friendly Bush administration.

The takeover announced Monday calls for the combined airline to be named Delta, remain based in Atlanta, and be run by Delta CEO Richard Anderson. If the share-swap becomes final, Delta shareholders will get a bigger company, while Northwest shareholders would get a 16.8 percent premium over Monday's closing stock prices. Based on those prices, the deal values Northwest at more than $3.6 billion.