What could the Fed buy with its $4.5 trillion?

The Federal Reserve may be raising interest rates Wednesday, but that's only the first step in what's bound to be a long return to normalcy.

The central bank will also have to decide what to do with the massive assets it picked up during the recession. Specifically, $4.5 trillion, mostly in Treasury notes as well as mortgage-backed securities that were bought up in an attempt to absorb some of the toxic assets.

The unconventional monetary policy of adding trillions to the balance sheet will require some unconventional methods of spending down. We thought we'd help Janet Yellen out and find out what $4.5 trillion could buy you.

The Fed could outright buy most companies on the S&P 500 — a full 341 separate companies at once. That's most of the companies, but counting from the bottom of the list when ranked by market cap.

If they just wanted to stick to the priciest, they could buy the 14 biggest companies: everything from Apple to Pfizer. That includes a lot of the nation's biggest firms, including AT&T, Facebook and GE.

The Fed has always made clear that its inflated balance sheet was a temporary policy to help stabilize the economy and that it would return to normal as stability returns. But no one knows how to do that and what the consequences of spending down the mass of funds will be.

Of course, that $4 trillion figure is total and doesn't take into account the size of the U.S. economy.

The Fed's balance sheet is now about 27 percent of GDP, far above the historical rate of around 6 percent. But that's nothing compared to many industrialized nations. The Bank of England and the European Central Bank both have higher asset-to-GDP ratios that the U.S., and assets at the Bank of Japan reached over 60 percent of GDP last year.

At the end of 2014, Switzerland's central banks' assets totaled 561 billion CHF, or about 87 percent of GDP.

In terms of sales, the Fed's balance sheet is nine times the size of Wal-Mart's annual sales, which topped the S&P in 2014 net sales. It's also 19 times the size of Apple's annual sales and 81 times those of Caterpillar, the company ranked 50th on that list.

The sheet is worth the sales of the bottom 433 companies on the index in net sales, or the same as the top 30.

With its massive pile of assets, the Fed could even match the top 30 companies' sales, and still have a few billion left over.

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