© ReutersSandy Weill's fortune was estimated at $1.3bn before Citigroup shares crashed in 2008
The call from the 79 year-old will cause a stir on Wall Street and in the City of London because Mr Weill engineered the 1998 deal that made Citigroup the world's largest bank. Hailed at the time, the merger of Citicorp and Travelers Group required the US government to repeal the Glass-Steagall Act, a law dating back to the Great Depression that prevented banks from both taking deposits from customers and gambling on the markets.
"What we should probably do is go and split up investment banking from banking," Mr Weill said in a television interview on Wednesday. "Have banks do something that's not going to risk the taxpayer dollars, that's not going to be too big too fail."
Mr Weill's intervention comes as the debate in the US over how to regulate the country's largest banks has been reignited by JP Morgan Chase's almost $6bn (£4.9bn) trading loss on complex derivative trades. JP Morgan chief executive Jamie Dimon, who was Mr Weill's chief lieutenant at Citi until the two fell out, has insisted that combining retail and investment banking is beneficial to consumers and businesses.
"I'm suggesting that they [the banks] be broken up so that the taxpayer will never be at risk, the depositors won't be at risk, the leverage of the banks will be something reasonsable," said Mr Weill, whose fortune was estimated at $1.3bn before Citigroup shares crashed in 2008. The bank eventually turned to the US taxpayer for a $45bn bail-out later that year.
Rather than split up the largest banks, the Dodd-Frank Act - America's signature piece of financial reform since the crisis - limited their activities and gave regulators more power. Critics of the reform say it has not removed the risk that taxpayers will ultimately have to bail-out the banks again should they get in trouble.
Comment: Not all of the banks that were given tax payer dollars have paid it back.