It's a tale of two stock prices. Since Monday's announcement of the deal involving Prudential Financial (NYSE:PRU) and Cigna (NYSE:CI), Prudential's stock price has increased slightly to just over $37, whereas Cigna's has fallen almost $3 to $53.12.

Prudential agreed to shell out $2.1 billion to purchase Cigna's retirement business. The price is all-cash and comes from the deep coffers of Prudential's insurance business.

This is certainly an investor-friendly deal for holders of Prudential stock. Essentially, the company is redeploying low-yield, low-risk cash into a segment with low risk but much higher yields. It also means Prudential gets much more scale, with its retirement assets growing to about $120 billion and the client base doubling to 2.2 million. In fact, the acquisition may help Prudential improve its credit rating to double A.

Prudential has spent about a year restructuring its business, which -- interestingly enough -- has made it much easier for the company to do the Cigna deal. Prudential sold off its troubled property-casualty lines and gave up a majority of its brokerage operations to Wachovia (NYSE:WB).

Cigna is also refocusing its business and has instituted a restructuring. The sale of the retirement business will be a critical move in the right direction. But it's still early in the process, so developments at the company warrant close attention.

Despite the volatile market of the past few years, the retirement planning business appears to have a bright future. Current estimates show the market at $16 trillion, which compares to the $48 trillion total wealth of U.S. individuals. Projections indicate that the retirement market is expected to grow to an astounding $39 trillion by 2012.

Even after the Cigna deal is closed, Prudential will still be in the minor leagues in the retirement plan business. With more cash in the company's coffers, though, who's to say the deals are done?

Tom Taulli is the author of six books on investing and finance, such as the Complete M&A Handbook (Random House). You can reach him at tom@taulli.com.