Say goodbye to Morgan Stanley Smith Barney. Say hello to Morgan Stanley Wealth Management.

Morgan Stanley (NYSE: MS) has just announced a deal with Citigroup (NYSE: C) to buy out part of the banks' joint brokerage enterprise, Morgan Stanley Smith Barney, for the low, low price of $13.5 billion. This will get the Wall Street perennial 14% of Citi's stake in MSSB, and paves the way for Morgan Stanley to buyout the rest.

The deal also paves the way for Morgan Stanley to further shift its business toward what it sees as the stable and profitable line of business that could eventually turn around its failing fortunes: wealth management.

But wait, there's more
It should be made clear that it's Morgan Stanley that thinks $13.5 billion is a low, low price. Citi was asking $22.5 billion, and the two banks had been arguing over the price and, therefore, holding up the deal for months. They finally let an independent arbitrator make the call, and it announced its decision of $13.5 billion on Monday evening. As part of the deal, Morgan Stanley also gets $5.5 billion in deposits.

The agreement also sets the stage for Morgan Stanley's eventual buyout of Citi's remaining 35% of MSSB, which Morgan Stanley will pay another $13.5 billion for. Morgan Stanley is required to complete the buyout by June 2015, at which time it will pick-up another $48 billion in deposits, too.

We can get you a great rate on a mortgage, Mr. Rockefeller
Of the two investment banks left standing at the end of the financial crash -- the other being Goldman Sachs (NYSE: GS) -- Morgan Stanley came out of the chaos much weaker, and has struggled more since. Post-crash, it just hasn't been able to find its legs again, while Goldman essentially got right back into its groove.

In the wake of 2010's Dodd-Frank financial reform legislation, specifically the Volcker Rule, which prevents banks from engaging in proprietary trading, America's big banks have been on the hunt for alternate lines of business to replace the missing profits. Goldman recently opened a private bank-within-a-bank to serve its wealthy clients around the globe, with services as basic as home loans.

Morgan Stanley has done something similar, and has also pinned a fair chunk of its hopes on wealth management, which is why this deal is so important. Wealth management services are rightly seen as more stable and less prone to market shocks than, say, credit default swaps. (If you're in doubt, just ask JPMorgan Chase's Jamie Dimon.)

The only big bank built to last
Morgan Stanley cut itself a good deal here, and CEO James Gorman is a smart guy, but the wealth management business is a competitive one. Hence, the smallish Morgan Stanley will have to go up against giants, like Bank of America (NYSE: BAC) and Wells Fargo (NYSE: WFC), with massive economies of scale working in their favor, and all competing for the finite supply of the world's wealthiest people. For investors in Morgan Stanley, let's hope the bank jumps on this golden opportunity and makes the most of it.

But for bank investors in general, and citizens everywhere, there's a trend in motion, one I've written about recently, and see as a very positive overall development post-crash -- regulation is working (if nothing else, the incoming Volcker Rule, a standout bit from the overly complex Dodd-Frank). Banks are seeking out and finding alternate ways to make money -- safer ways, like private banking and wealth management. It means a more stable banking system for everyone and, ultimately I think, more transparent, easier-to-understand banks as investments.

But believe it or not, there's still a big bank out there right now that's a good investment. It's one that managed to avoid many of the pitfalls that befell its peers in the run-up to the financial crash. As such, it's one of the few big banks that The Motley Fool can still, in good conscience, recommend as an investment. Learn all about it in this special free report, The Only Big Bank Built to Last. Download it while it's still available by simply clicking here now.