You wouldn't know it from watching their stocks, but the biggest US banks just had a banner year.

JPMorgan Chase ( JPM ), Bank of America ( BAC ), Wells Fargo ( WFC ), Citigroup ( C ), Goldman Sachs ( GS ) and Morgan Stanley ( MS ) brought in more than $120 billion combined in profit last year, the result of President Donald Trump's corporate tax cuts and a booming economy.

That's a record showing. It also dwarfs the amount they made in 2017, when many banks faced large, one-time charges related to tax reform.

Those results highlight the degree to which bank shares have diverged from actual business performance. The sector's stocks had a dismal 2018, weighed down by concerns about rising interest rates, the shrinking difference between short-term and long-term bond yields, and global issues such as trade and Brexit.

But fears about slowing economic growth ahead take focus off what's happening right now: American banks are making more money than ever.

The largest players had mostly good news to share when they reported earnings for the final three months of 2018 this week.

One area that's being closely watched is how rising interest rates will affect banks.

Typically, higher rates let banks charge more interest on loans, while forcing them to grow what they pay out on deposits. But the spread between loan earnings and deposit costs was better than expected last quarter, according to Fred Cannon, director of research at Keefe, Bruyette & Woods.

"Deposit costs are rising," he said. "But they didn't go up quite as much as people expected."

One dark spot was trading revenue. Global markets veered wildly in December. Instead of encouraging trading, this volatility appears to have spooked investors. Repeat sell-offs may have encouraged them to stay on the sidelines or cash out investments without making new ones.

Bond trading revenue suffered as a result. At JPMorgan, it fell 16%. At Goldman Sachs, which beat analyst expectations overall, trading revenue from the fixed income unit plunged 18%.

But bank executives brushed this off as a one-time problem, noting that January trading so far has been much more stable than December.

"I honestly couldn't care less," JPMorgan CEO Jamie Dimon said Tuesday. He pointed to the company's strong performance in other areas, such as loans and credit cards.

Loan growth was generally solid, though Cannon pointed out this is not just about rising demand. He said market volatility played a role, and he encouraged banks to keep some loans on their balance sheets that would have otherwise been sold.

Despite healthy numbers overall, bank leaders clearly felt the need to reassure investors about the state of the economy. The International Monetary Fund and the World Bank have cut their growth forecasts for 2019, and concerns about a slowdown appear to be growing.

That matters for banks since profits are closely tied to the economy. They suffer when growth slows and businesses are scared to borrow, and become especially vulnerable when a recession hits and some customers aren't able to pay back loans.

Bank leaders said that while growth may slow, what they're seeing doesn't necessarily indicate near-term trouble.

"From what we see, economic growth is stronger and more resilient than recent market volatility would indicate," Citigroup CEO Michael Corbat said Monday.

Dimon took pains to note that even if a recession were to hit, it would look very different from the one that followed the 2008 financial crisis. "Credit is pristine," he said during a Tuesday call for investors.

While some non-bank lenders could be in trouble, the quality of loans on JPMorgan's books is strong, Dimon added.

"We're not immune to what goes on in the economy," Dimon said. But "it won't be anything like you saw last time for much of the large banks."

One sticking point is the partial government shutdown, which could drag down economic growth in the first quarter of 2019 as it stretches into its 28th day.

The effects of the shutdown will hit banks eventually. The closure cramps lending and could even hurt capital markets activity by preventing companies from going public.

"If the government shutdown continues, nobody's home at the [Securities and Exchange Commission]" to approve IPOs, Cannon said.