The tax break expected to slash what three of the biggest Wall Street banks have to pay the Internal Revenue Service may cost them more than $20 billion first.

A reduction in the top corporate rate to 21 percent from 35 percent, which will buoy lenders' bottom lines in 2018, also lowers the value of paper assets that some have held on to for years. "Deferred tax assets," or losses from previous years that can be used to reduce payments later, will now have to be marked down because they're worth less under the lower rate that's a signature feature of the Tax Cuts and Jobs Act, attorneys and Wall Street analysts said.

That may curb earnings by $17 billion at Citigroup and up to $1.7 billion at Goldman Sachs, both of which are based in New York and are slated to report fourth-quarter earnings this week. Profit at Charlotte, N.C.-based Bank of America may be reduced by $3 billion, estimated Jason Goldberg, an analyst with Barclays Plc.

Rivals who were able to defer payments from prior years, meanwhile, including JPMorgan Chase and Wells Fargo, got a boost at the end of last year by marking down those obligations. Their competitors will eventually benefit, too, keeping cash that can be invested in the companies themselves, employees, and communities.

That's precisely what the overhaul, the most significant in decades, was designed by President Donald Trump and Congressional Republicans to do: buoy the economy by making the U.S. more competitive with foreign countries and freeing corporate cash that could be spent on expansion.

The lenders that have reported earnings so far are generally bullish on the law's prospects of success, even if it caused some short-term pain. JPMorgan, for instance, took a $3.7 billion hit on assets parked overseas because of a provision that assesses a mandatory one-time fee of 15.5 percent on cash holdings and 8 percent on others.

After paying it, however, companies can bring the assets back to the U.S. at any time, with no further penalty. Under the old system, they would have been charged the applicable U.S. tax rate any time they did so.

"The modernization of the U.S. tax code is a significant step forward for the country and a big win for the economy," JPMorgan Chief Financial Officer Marianne Lake told investors on Friday.

"However, clients are still digesting the tax bill," and much like the Federal Reserve's current round of interest-rate increases, "we haven't seen this movie before," she said. "We'll have to see how it plays out."

For now, JPMorgan is putting together a comprehensive plan that will use its savings to benefit employees, customers and communities, Lake said.

"We think it’s time that all of America share broadly, and we’re going to have things that we think are good for some employees," CEO Jamie Dimon said, "and, I think, also for sustainable growth for communities around the world."

Bank of America, meanwhile, has said it would award a $1,000 bonus to 145,000 of its employees, almost 70 percent of the company's workforce at the end of 2017. San Francisco-based Wells Fargo committed in December to raising the minimum wage for its employees to $15 an hour if the tax overhaul passed, along with making $400 million in donations.

"The feedback that we've been getting from our customers is that we should all be cautiously optimistic on the impact of the tax reform," Wells Fargo CEO Tim Sloan told investors last week. "There have been millions of employed folks across the country that have gotten pay raises and bonuses and the like, and I think that's a net positive for economic growth."