Nearly one-third of the bank's office space is to be taken up by two trading floors, according to the developer's news release in December, but Weiss said it was not yet clear how big the dealing operation would be.

"It was important to have the space that can be built out into a trading operation in the hope that we continue to grow," he said. Wells Fargo's investment banking and trading operations are currently housed in 350,000 square feet spread across four separate buildings in New York.

That represents a big leap for a bank seen as a sleeping giant in the U.S. investment banking industry. It has the balance sheet and lending relationships to be a top player, but a culture more in touch with Main Street than Wall Street.

Wells Fargo's bosses have made fun of Wall Street's self-importance. Chief Executive John Stumpf, a farmer's son from Minnesota, likes to say he prefers kitchen tables to "league tables" - the rankings used by investment banks to measure their standing.

But as Wall Street rivals exit and low interest rates force banks to look for more sources of revenue, Wells Fargo's current and former executives see more opportunities.

"I had been very vocal in saying I didn't believe investment banking was culturally compatible with our ethics and our business model," said former Wells Fargo CEO Richard Kovacevich.

"But as a result of the financial crisis, with investment banks becoming banks or being bought by them, the culture has changed," said the 72-year-old banker, who retired in 2009 but still has an office at Wells Fargo and meets with big investment bank clients.

Aggressive Competition

Rivals have noticed the bank's ramped-up presence. JPMorgan CEO Jamie Dimon told Bloomberg earlier this month Wells Fargo was "very actively, very aggressively, and very successfully building its U.S. investment bank."

This month, Wells Fargo was named sole adviser to TransCanada Corp on its acquisition of Columbia Pipeline Group, a deal worth $13 billion including debt, putting it on track for its biggest fees from a single deal since at least 2000, according to data from Thomson Reuters and Freeman Consulting Services.