The Wall Street that shaped the financial world for two decades ended last night, when Goldman Sachs Group Inc. and Morgan Stanley concluded there is no future in remaining investment banks now that investors have determined the model is broken.

The Federal Reserve’s approval of their bid to become banks ends the ascendancy of the securities firms, 75 years after Congress separated them from deposit-taking lenders, and caps weeks of chaos that sent Lehman Brothers Holdings Inc. into bankruptcy and led to the rushed sale of Merrill Lynch & Co. to Bank of America Corp.

The announcement paves the way for the two New York-based firms, both of which will now be regulated by the Fed, to build their deposit base, potentially through acquisitions. That will allow them to rely more heavily on deposits from retail customers instead of using money borrowed in the bond market — the leverage that led to the undoing of Bear Stearns and Lehman.

Morgan Stanley has taken $15.7 billion of writedowns and losses on mortgage-related securities and other types of loans since the credit crunch started last year. Goldman’s tally stands at about $4.9 billion. While both companies have remained profitable and avoided money-losing quarters suffered by Lehman and Merrill Lynch, their revenue from sales and trading and investment banking has been declining this year.

As bank holding companies, Goldman and Morgan Stanley will no longer be required to mark all of their assets to the current market values. Assets held in the bank divisions of the firms don’t have to be valued at market rates, potentially allowing the companies to allow further writedowns on the value of their holdings.