For Delta and Northwest to complete their combination to create the world's largest airline, they'll have unions to cajole, politicians to placate and antitrust regulators to convince — as well as persuading investors who have panned the deal to change their minds.

Shares of both carriers fell sharply Tuesday after executives said they currently do not plan to cut the number of U.S. flights beyond what they already disclosed individually — something analysts saw as limiting the cost saving or revenue increases from higher fares the airlines could get from the deal.

Two of Northwest's largest unions also immediately declared their opposition to the long-in-the-works deal, announced late Monday after several months of talks.

Executives brushed off the issues, saying they are highly confident they will be able to consummate the deal and integrate the two carriers.

"Bottom line is, we think it's a really good fit," Delta Chief Executive Richard Anderson, who will head the combined airline, said Tuesday during a conference call with analysts.

Delta and Northwest executives 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. They are trying to avoid repeating what happened in 2001, when an attempted merger of United Airlines and US Airways fell apart amid antitrust concerns.

The share-swap agreement announced Monday calls for the combined airline to be named Delta, remain based in Atlanta, and be run by Anderson. If the deal 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 agreement valued Northwest at more than $3.6 billion. However, shares of both companies fell Tuesday, reducing the deal's value of Northwest to $3.3 billion. Northwest fell 48 cents, or 4.3 percent, to $10.74 while Delta lost $1, or 9.5 percent, to $9.48.

Investors had urged a combination of the carriers on the premise of further domestic capacity cuts, which could lead to higher ticket fares and more revenue for the airlines.

Both airlines previously announced domestic capacity cuts for this year, and Delta suggested no more are in the works — though it didn't rule out more in the future if fuel prices continue to rise.

"We feel like we have pruned the domestic system for each respective system," Ed Bastian, Delta's president and chief financial officer, said on the conference call.