The Federal Reserve has been under attack recently, most prominently by Donald Trump.
But what doesn't get a lot of attention is the massive profit it earns for U.S. taxpayers.
Last year the Fed poured a record $117 billion back into U.S. coffers, a record high. That money gets spent on everything from highway construction to the military and food stamps.
In the last decade, its payments to Treasury have totaled nearly $700 billion. Since the bank's operating expenses are only about $4 billion a year, it's an incredibly profitable business.
"We'd all like to have this kind of business," said Frederic Mishkin, a former Fed governor who is now a professor at Columbia University.
For the most part, the Fed makes money by collecting interest on the U.S. Treasuries and mortgage-backed securities in its portfolio.
The bank also has other sources of income, such as the fees it earns for providing banking services to commercial banks. But the overwhelming majority of the Fed's income comes from interest on its holdings.
The Fed hasn't always racked up such staggering profits. They're driven by the fact that the Fed's holdings grew to unprecedented levels following the 2008 financial crisis. That's when it started pumping hundreds of billions in cash into the economy by making massive purchases of Treasuries and mortgages.
The Fed stopped making to those purchases two years ago, and the interest rates paid on that U.S. debt have remained low. But the holdings are so large that the Fed collected a record $63.3 billion in interest on Treasuries last year, along with $48.9 billion in interest from mortgages. It will take years for those holdings to shrink back to normal levels.
"The Fed's profit is unusually high," Mishkin said. "Eventually that should that disappear." But in just over a century of doing business, it's always turned at least some profit -- it was earning about $30 billion a year in the years leading up to the financial crisis.
The Fed has often been criticized by Trump and other Republicans for doing so much to try to pump up the economy for so long.
But Mishkin said that even if, under a Republican administration, the Fed drastically cut the central bank's holdings and raised the Fed funds rate, it would still make billions of dollars a year.