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Check out which companies are making headlines before the bell:

Morgan Stanley — The company earned 81 cents per share for the fourth quarter, well above estimates of 65 cents a share. Revenue also beat forecasts. Morgan Stanley's results were helped in part by a surge in trading activity after the presidential election.

UnitedHealth Group — The health insurer earned an adjusted $2.11 per share for the fourth quarter, 4 cents a share above estimates. Revenue also beat Street forecasts. UnitedHealth saw strength in its pharmacy benefit management business and noted a large increase in medical benefits customers during 2016.

Wal-Mart — The retail giant said it planned to add about 10,000 U.S. retail jobs, as it opens new stores and expands existing Walmart and Sam's Club locations. The company also said its moves would provide about 24,000 construction jobs.

Tiffany — The luxury goods retailer reported a 4 percent drop in holiday-period same-store sales, pointing to a decline in consumer spending. It also said sales at its flagship New York location were hurt by traffic disruption near Trump Tower, and that it does not anticipate a significant improvement in economic conditions this year.

Twitter — UBS downgraded the stock to "neutral" from "buy," saying the company faces a number of operating challenges.

Netflix — Netflix was upgraded to "buy" from "neutral" at Mizuho, with the price target increased to $152 per share from $112. Mizuho points to the possibility of material growth for Netflix in international markets.

Walt Disney — Disney was upgraded to "buy" from "neutral" at Goldman Sachs, citing optimism about Disney's 2018 film offerings among other factors.

Nordstrom — Nordstrom was downgraded to "hold" from "buy" at Stifel Nicolaus, with Stifel expecting weaker-than-anticipated holiday season results for the retailer.

Chipotle Mexican Grill — The stock was downgraded from "overweight" to "neutral," citing labor challenges for Chipotle and other restaurants in the fast-casual category, as well as an oversupplied market.

Sony — Sony Entertainment division Chief Executive Michael Lynton is stepping down to become chairman of Snapchat parent Snap Inc. He'll step down on February 2, but will remain co-CEO for six months to help find a successor.

Facebook — Facebook is trying to head off legislation in Germany that would subject it to tougher regulation. Top managers including COO Sheryl Sandberg visited Germany over the weekend, with the company pledging to take more steps to fight fake news and hate speech.

Reynolds American — Reynolds and British American Tobacco struck a revised takeover deal that boosts a prior bid by more than $2 billion. BAT will pay $29.44 per share and a little more than half a BAT share for each Reynolds share that it doesn't already own.

General Motors — GM will announce a $1 billion investment in several U.S. factories, according to multiple reports, creating more than 1,000 new jobs.

Syngenta — Chief Executive Officer Erik Fyrwald tells CNBC that he expects regulatory approval for the planned $43 billion takeover of the chemical maker by ChemChina.

Clayton Williams Energy — Clayton Williams will be bought by Noble Energy in a $2.7 billion cash and stock deal that gives Noble 120,000 acres of oil properties in West Texas.

Luxottica — Luxottica will merge with France's Essilor in an all-stock deal that creates a global eyewear seller with annual sales of more than $16 billion.