But there’s a bigger risk-free payout the Fed makes to big banks, one set to rise exponentially as the economy improves. In fact, according to the Congressional Budget Office, hundreds of billions of dollars that would otherwise go into the federal Treasury will leak out to banks, including branches of foreign banks, in the coming years. If Congress needs to find money to pay for new programs, they could cancel the Fed’s recent practice of paying interest on bank reserves.

For nearly 100 years, the Federal Reserve managed the nation’s monetary policy without paying interest on reserves, including the 10 percent of the value of loanswhich banks are required by law to park at the Fed. But in 2006, Congress passed the Financial Services Regulatory Relief Act, authorizing interest payments. It was actually an old idea first promoted by conservative economist Milton Friedman.

Friedman thought that required reserves without compensation constituted a hidden tax on the financial industry. He also believed the strategy would make it easier for central banks to engage in monetary policy. If the Fed offered an interest rate on excess reserves just above the federal-funds rate (a.k.a. the rate banks use to lend to each other), then it makes more financial sense for banks to leave their money there. It sets a floor for the federal-funds rate, in other words, giving the Fed more control over its range. It also helps the Fed expand its balance sheet, critical to engaging in monetary interventions like quantitative easing.

Under the 2006 law, interest on reserves wasn’t supposed to kick in until 2011, but Congress moved up the date three years when it passed the law authorizing the Troubled Asset Relief Program (TARP). The Fed set the interest rate on all reserves at a skinny 0.25 percent, which produces a small payout on required reserves. But excess reserves above the 10 percent requirement, which banks never left at the Fed until 2008, exploded as the Fed’s balance sheet expanded. From virtually nothing seven years ago, excess reserves hover around $3 trillion today.

Who owns these excess reserves? As the Cleveland Fed noted in a report last week, more than 80 percent come from the top 100 largest banks. U.S. branches of foreign banks, primarily from the European Union, have about $1 trillion in excess reserves parked at the Fed.

The Fed’s audited financial statement indicates that they have paid banks $25.2 billion in interest on reserves from 2008 to 2014. That number jumped from $2.1 billion in 2009 to $6.7 billion in 2014, a three-fold increase. The entire time, the interest rate has been the same: 0.25 percent. But that’s subject to change.

As the economy improves, the Fed is clearly angling to raise the federal-funds rate, which has been stuck around zero since 2008. Fed officials have already indicated they will accomplish this mostly through recalibrating interest on reserves. At theirSeptember 2014 policy meeting, Fed Chair Janet Yellen said the central bank would “move the federal-funds rate into the target range … primarily by adjusting the interest rate it pays on excess reserve balances.” While the interest rate on required reserves may stay constant, the Fed would raise the interest rate on excess reserves, allowing interbank lending only to rise so far.

In effect, interest on excess reserves is equivalent to the federal-funds rate. And the higher the interest rate goes, the more money banks make from the Fed. You can see this most clearly in Congressional Budget Office (CBO) projections of Fed remittances.

Any money the Fed makes on investments gets returned to the federal Treasury. And business has been good for the Fed of late. They remitted $99 billion in 2014 and a projected $102 billion this year. But CBO’s latest update predicts that number will fall drastically, to $76 billion in 2016, $40 billion in 2017, and just $17 billion in 2018. The lion’s share of the difference comes from the Fed paying out their earnings to banks, with higher interest on reserves as they hike rates.

While it’s hard to pinpoint the totals because the CBO doesn’t separate out interest on reserves, by marking the difference between 2015 and subsequent years we can estimate that the Fed could deliver anywhere from $20 billion to $50 billion a year to banks, risk-free. That’s an enormous amount of money, based on the claim that interest on reserves is somehow an indispensible strategy for monetary policy, even though the Fed thrived for 91 years without such a tool.

This shift in how monetary policy is conducted occurred with practically no debate. Fed officials are reportedly worried about the “optics” of their exit plan, with its unjust enrichment of the largest banks. But outside of a few libertarians, nobody has raised alarms yet.

One progressive group that’s challenged the Fed from the left was stunned to learn that, in addition to depressing the economy, an interest-rate hike would have a secondary effect as a silent bank bailout. “Clearly this is under-covered, because I haven’t heard about it,” said Ady Barkan with the Center for Popular Democracy, director of Fed Up, a grassroots organization pushing the central bank to adopt pro-worker policies. “But we shouldn’t be shocked. It is the rule that the Fed prioritizes helping banks, and has over the last seven years.”

There are other ways to control monetary policy besides interest on excess reserves, unless you believe that the Fed was impotent from 1917 to 2008. For instance, the Fed could reduce their balance sheet, rather than letting it contract through attrition, the current strategy. That would reduce the money supply, which shows what a pickle the Fed has gotten itself into with its expanded balance sheet. But the Minneapolis Fed, at least, downplayed the risks of gradual asset sales into a global market.

Another option is to hold off on raising rates, allowing the balance sheet to slowly contract and encouraging banks to recirculate excess reserves into the economy by creating favorable conditions for more profitable investments. “It’s incomprehensible to us to think that the economy is getting too healthy too quickly,” said Barkan of Fed Up.

Members of Congress, who created this mess by authorizing interest on reserves, could take it away too, and in so doing could create a large pay-for that could be transferred into productive projects. You could potentially fund an entire six-year highway bill simply by eliminating interest on reserves.

We don’t even know if the Fed’s rate-raising strategy will work without drawbacks, as it’s never been tested. But if “working” equals paying the largest banks hundreds of billions in unearned money, the Fed should figure out something else.