Just give investors what they want, okay?

The Federal Reserve kept key interest rates unchanged following its May policy statement on Wednesday, but failed to provide any new details on the future of its monstrous $4.5 trillion balance sheet. 

This is what the Fed said about its balance sheet in the statement:

"The Committee is maintaining its existing policy of reinvesting principal payments from its holdings of agency debt and agency mortgage-backed securities in agency mortgage-backed securities and of rolling over maturing Treasury securities at auction, and it anticipates doing so until normalization of the level of the federal funds rate is well under way."

This was the same language as the March statement.

The reason investors were hoping for more details about the balance sheet is because the issue came up in the minutes of the March statement, released in April. 

At that time, the Fed hinted that a change to its reinvestment policy is likely. Currently, the Fed reinvests the securities it holds, maintaining the size of its balance sheet. Some analysts expect the Fed to taper or halt those reinvestments.

But only until it gets interest rates up to a certain level. 

"The Fed doesn't want to put the cart before the horse and talk about the balance sheet until they feel they've done more work on the rate side," said Nick Colas, chief market analyst at Convergex, who  expects more details on the future of the central bank's balance sheet during Chair Janet Yellen's annual speech in Jackson Hole, Wyo. in late August.  

Unwinding its balance sheet may have the same impact on the markets as raising interest rates. 

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