This week's earnings schedule includes a trove of large banks such as JPMorgan Chase and Wells Fargo, as well as reports from Netflix, IBM and Honeywell International.
Analysts expect companies in the S&P 500 to report a 4.1 percent drop in third-quarter results, according to Factset.
About 20 minutes into trading, the Dow Jones Industrial Average was down 0.1 percent at 26,791.02.
The broad-based S&P 500 also dropped 0.1 percent to 2,966.70, along with the tech-rich Nasdaq Composite Index, which was at 8,047.64.
Major indices gained more than one percent Friday ahead of an announcement of a "phase one" trade agreement between the US and China, and Washington's announcement that it would hold off on a tariff increase scheduled to take effect Tuesday.
But sentiment about the agreement shifted over the weekend following more subdued commentary in the Chinese press as analysts focused on the fact the deal did not remove any existing tariffs on hundreds of billions of dollars of trade between the countries.
US Treasury Secretary Steven Mnuchin said Monday the two sides would continue to hold talks by phone this week and next.
Among individual companies, Boeing slipped 0.2 percent after announcing late Friday that Chief Executive Dennis Muilenburg would lose his title as chairman but remain on the Board of Directors.
Some analysts said the move could be a prelude to Muilenburg's eventual departure as CEO as the crisis over the 737 MAX drags on.
The plane has been grounded since March following two deadly crashes.