The S&P 500 closed lower Wednesday as the Federal Reserve left interest rates unchanged, even as two policymakers dissented—the first double dissent since 1993—highlighting growing divisions over the future of monetary policy.

The S&P 500 rose 10.4 points, or 0.16%, at the open to 6,381.23​, while the Nasdaq Composite rose 42.1 points, or 0.20%, to 21,140.397 at the opening bell.