U.S. stocks lost steam Tuesday as U.K. Prime Minister Theresa May signaled that a "hard Brexit" was on the horizon, shutting access to the EU's single market. May also said a new trade agreement with the European Union would be negotiated. She reiterated the importance of the UK's control over immigration.

Morgan Stanley (MS - Get Report) is out with fourth-quarter results. Earnings of 81 cents a share topped estimates of 65 cents. Morgan Stanley's fixed-income revenue surged to $1.47 billion, compared to $550 million in the same quarter a year ago.

Rivals Bank of America (BAC - Get Report) and JPMorgan Chase (JPM - Get Report) also reported surges in trading revenue amid volatile markets surrounding the U.S. presidential election.

Shares of UnitedHealth (UNH - Get Report) were in focus after the company reported adjusted earnings of $2.11 a share during the fourth quarter, beating estimates of $2.07. Revenue of $47.5 billion eclipsed estimates of $47.1 billion, as the company provided health benefits to 2.2 million more people.