President Obama is set to propose new regulations today for large Wall Street firms. The measures would limit the size of large banks as well as the practice known as proprietary trading in which commercial banks trade financial securities from their own commercial accounts. Former Federal Reserve chair Paul Volcker has been a leading advocate for the proposals. He says it would help undo some of the damage of the 1999 repeal of the Glass-Steagall Act, which had ensured the separation of commercial and investment banking.