The Fed is expected to keep monetary policy unchanged when it unveils its decision Wednesday following a two-day meeting, but the announcement will be scrutinized for the likelihood of a December rate increase.

Looming over the decision is President Donald Trump's upcoming announcement Thursday of his pick to lead the US central bank, likely replacing current Chair Janet Yellen.

Earnings were mixed early Tuesday, with reports from Apple and Facebook due later in the week.

About 20 minutes into trading, the Dow Jones Industrial Average was unchanged at 23,348.44.

The broad-based S&P 500 added 0.1 percent to 2,574.83, while the tech-rich Nasdaq Composite Index advanced 0.3 percent to 6,717.84.

Cereal company Kellogg shot up 7.7 percent after third-quarter net income edged higher to $297 million. Chief executive John Bryant said sales were boosted by direct-store deliveries and that the company was on track to fulfill its 2017 targets.

Pfizer dropped 1.6 percent despite reporting that third-quarter net income more than doubled to $2.8 billion. Goldman Sachs said in a note that sales of some of the pharmaceutical giant's most important came in below expectations.

Under Armour plunged 11.5 percent after reporting third-quarter earnings fell 57.7 percent to $54.2 million on sharply lower North American revenues.