JPMorgan Chase is again fighting back against calls by many pundits and analysts to break up the megabank.

Speaking at its annual investor day on Tuesday, Chief Financial Officer Marianne Lake laid out JPMorgan's case for why it is best to keep the company whole.

"Our synergies are real. … No peer enjoys them at the same level," Lake said.

"Scale has always defined the winner in banking," she said near the beginning of her overall presentation about the company's health, later adding that JPMorgan is "the most durable banking franchise in the world, with benefits only afforded to the leaders."

Analysts and investors have been pressuring the company to consider a breakup given its high expenses, capital constraints imposed by regulators and recent stock performance. Essentially, analysts say JPMorgan's performance has not lived up to the proposition that the company benefits from its size.

The company included a slide in its presentation entitled, "Implications of Separation Scenario." A "modest portion" of revenue would be lost and that would be a "small negative," it said.The separated companies would find it harder to make investments that would protect them against downturns, and the company could lose its leadership positions in key markets, the company said.

Breaking off, say, Chase Bank from the rest of J.P. Morgan would create companies that retain some scale, but they would need to invest in ancillary businesses and corporate functions and that would be a "meaningful negative" because of redundancies. Lake said that would mean two cybersecurity programs, two data functions, two boards and other overlaps.

"Two investor days," she said, with the crowd of investors and analysts laughing. The costs are "not trivial."

Lake also said there would be roughly $15 billion less in excess capital available to shareholders, because the Federal Reserve's comprehensive capital analysis and review (CCAR) of the bank "would be the binding constraint."

The company also laid out its three-year goals. It is aiming for a 15% return on tangible common equity and an improvement in its efficiency ratio to 55% from 60% in 2014 (excluding its legal expenses) . The drivers of that would be $2 billion in expense cuts from its consumer and community bank business lines and $2.8 billion from its corporate and investment bank.

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