Morgan Stanley and Citigroup Inc have launched their brokerage joint venture at least a month ahead of schedule, the companies said on Monday.

The combination of Morgan Stanley's Global Wealth Management Group with Citi's Smith Barney into what is by some measures one of the world's largest wealth management businesses was initially slated to close in the third quarter.

With the deal's completion, Citi expects a pre-tax gain of $10.9 billion, boosting its tangible common equity by an estimated $7.8 billion.

The companies have said they each expect to realize $1.1 billion in savings from the joint venture after full integration.

(Reporting by Steve Eder; editing by John Wallace)