US banking and energy shares weak
The Dow Jones Industrial Average and the S&P 500 closed lower, hit by falls in energy and financial shares.
Having come close to breaking the 20,000 barrier on Friday, the Dow lost 74 points to end at 19,888. The S&P 500 fell 8 points to close at 2,268.
However, the Nasdaq climbed 10 points to finish at 5,531.
With a 1.5% fall, Exxon Mobil was the biggest faller among Dow components. Energy shares were hurt by a sharp fall in the price of crude oil.
US crude lost more than $2 a barrel, or 4%, to close at $51.87, as worries re-emerged about an oversupply in the oil market.
Banking shares were weak, with Goldman Sachs losing 1%. Banks begin to report quarterly results later this week.
On Friday both JP Morgan and Bank of America are due to report results.
JP Morgan shares were little changed and Bank of America was down 0.5%.
"We're waiting for the roll-out of earnings and the initial forays of the Trump administration," Stephen Massocca, chief investment officer of Wedbush Equity Management.
"I don't see significant moves in the market until those events unwind," he said.