Wells Fargo, widely regarded as the industry's least complex megabank, has recently made big moves into the volatile world of investment banking. But John Shrewsberry, the company's chief financial officer, cautioned against reading too much into it.

Speaking Tuesday at an industry conference, Shrewsberry downplayed the unit's recent success when asked about its plans to ramp up growth in investment banking.

In the first quarter, Wells ranked No. 3 in the industry for investment banking transactions in the U.S. — ahead of Citigroup and Goldman Sachs. The company has also steadily increased its market share.

"It depends on what you mean by investment banking," Shrewsberry replied.

Any future growth in the business won't "change the character" of the company's balance sheet, he added.

Shrewsberry's comments illustrate the delicate balancing act facing Wells as it expands beyond its traditional bread-and-butter retail business and into the more risky and complicated world of Wall Street finance.

The self-described "Main Street bank" entered the investment banking market during the financial crisis, through its 2008 purchase of Wachovia. Since then, it has slowly taken a bigger piece of the market, as some of its larger competitors have scaled back.

During the first quarter, the company's share of the U.S. investment banking market was about 5%, compared to about 4% for the 2015 calendar year.

Investment banking also generated about 3% of the of the company's fees. Still, revenue from the unit plunged 26% from a year earlier, to $331 million, amid volatility in the market.

At the conference, Shrewsberry said Wells is reluctant to use its balance sheet to attract business from hedge funds and asset managers. Because of that, prime brokerage likely will not grow into an "enormous business" for Wells.

"Using our balance sheet comes at a cost," he said. "We are trying to generate a 12%, 13%, 14% return on equity, and the financing business doesn't do that."

Wells does plan to continue expanding its capital raising and M&A advisory business to its wholesale customers, according to Shrewsberry.

The comments echo Wells Fargo's previous line on its investment business. Jon Weiss, head of Wells Fargo Securities, said in a speech at the company's investor day last month that he has seen "palatable" momentum in the business.

Over 43% of the company's wholesale corporate and commercial clients used an investment banking product in the past year, Weiss said.

But Wells Fargo has maintained that it has a handle on the financial and reputational risks that come with the business.

"I will use an improper word: You can't prostitute your balance sheet to get a fee," Tim Sloan, Wells' president and chief operating officer, said at the company's investor day. "That just doesn't make long-term sense."

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