About 15 minutes into trading, the Dow Jones Industrial Average stood at 27,221.32, up 0.1 percent.

But the broad-based S&P 500 slipped 0.2 percent to 3,020.78, and the tech-rich Nasdaq Composite Index shed 0.5 percent to 8,290.23 -- both retreating from record closes on Friday.

The cautious start to the trading week came ahead of a trove of market-moving events in the coming days.

The Fed is expected to cut interest rates on Wednesday for the first time in a decade, but the size of the cut and the question of whether the US central bank will have to deliver more stimulus this year remain subject of intense debate.

Earnings also will continue to be in focus in the last of three especially heavy weeks of reports on quarterly results. This week's slate includes Apple, Procter & Gamble and Exxon Mobil.

Other significant events this week include the resumption of trade talks between the US and China, the US jobs report for July, and the second round of debates for the crowd of early Democratic presidential candidates.

Among individual companies, generic drug company Mylan shot up 14.3 percent as it announced plans to combine with Pfizer's non-patent drug division. Dow-member Pfizer fell 1.1 percent.