The banks’ preparations for the hard times ahead hit their profits hard in the last quarter.

JPMorgan’s net income fell to $2.9 billion from $8.5 billion for the last quarter of 2019 and $9.2 billion for the same period a year earlier — with the bank’s new reserves essentially the difference. Wells Fargo reported a steep drop in profit to $653 million from $5.9 billion during the same period in 2019.

JPMorgan expected consumer loans — most of them credit cards — to lose $4.4 billion while commercial loans to businesses in real estate, retail and oil and gas could lose $2.4 billion, according to its estimates. And Wells Fargo said $1 billion of its potential losses could come from loans to consumers and small businesses.

The reserve-building activities spooked investors in both banks. Despite overall increases in the values of the major stock indexes on Tuesday, Wells Fargo shares were down by almost 4 percent and JPMorgan by 2.7 percent at the end of trading.

But there were some bright spots, particularly at JPMorgan.

The bank reported that revenue from trading things like foreign currencies, bonds and government debt rose 34 percent from a year earlier. Stock-trading revenue was 28 percent higher. Over all, revenue in the bank’s Wall Street markets division reached $7.4 billion, a record.

And there is Mr. Dimon’s health. Mr. Dimon underwent emergency heart surgery in March, but returned to work on April 2. He said the operation had not changed his outlook for his future; he said he felt good and under no pressure to retire.

“I’ve always liked working,” he said. “I think people having a purpose in life is a good thing.”

Both banks reported their corporate clients were pulling cash from the lines of credits they maintain to deal with the economic effects of the outbreak.

JPMorgan’s chief financial officer, Jennifer Piepszak, said on a call with reporters that corporate customers had taken cash out of their revolving credit lines at an unusually high rate. Mr. Dimon added that the rate was twice what it had been during the 2008 financial crisis.