In politics, it is called flip-flopping. In banking, it is called postcrisis regrets.

For years, Sandy Weill aggressively pushed a "bigger-is-better" philosophy in banking, turning Citigroup into a financial behemoth through a series of ever-larger deals.

Now, the empire builder wants to break up the banks.

On Wednesday, Weill called for a wall between a bank's deposit-taking operations and its risky trading businesses. In other words, he would like to resurrect the regulation that he once fought.

"What we should probably do is go and split up investment banking from banking," Weill, the former chief executive of Citigroup, told CNBC. "Have banks do something that's not going to risk the taxpayer dollars, that's not going to be too big to fail."

Since the financial crisis, some elder statesmen have pushed to reinstate some form of the Glass-Steagall Act, the 1933 law that separated commercial banks from investment banks.

In 2009, John Reed, who with Weill forged the megamerger that created Citigroup, apologized for creating a lumbering giant that needed multibillion-dollar bailouts from the government.

Philip Purcell, the former chief executive of Morgan Stanley and David Komansky, the onetime leader of Merrill Lynch, two other main figures in the fight to repeal Glass-Steagall, have echoed similar concerns about deregulation.

But the comments of Weill — arguably the most powerful banking voice behind the effort to dismantle Glass-Steagall — have particularly drawn the industry's attention.

Weill has largely kept silent during the debates over financial regulation. Even now, he has refused to say that the banking-supermarket model was flawed.

"I think the earlier model was right for that time," he said on CNBC. "I don't think it's right anymore."

Not all of these banking elders have spoken out of concern for the safety of the global financial system. Both Weill and Purcell noted that cleaving apart big banks would improve their stock-market values.

But their sentiments are not necessarily shared by their successors. Jamie Dimon, Weill's longtime protégé who now runs JPMorgan Chase, turned aside questions about the bank's size after the latest earnings.

"There's huge strength in this company that units get from each other," Dimon said, who added that splitting up JPMorgan would affect "very short-term stuff."