Investors will parse Yellen's language to determine whether the Fed will begin unwinding its balance sheet in September. The central bank previously said that was a move that it would implement "relatively soon," provided the economy expands as expected. Paring the Fed's sizable assets would likely tighten monetary conditions in the same way an interest-rate hike would. Another rate increase isn't expected until December at the earliest.
The Dow Jones Industrial Average fell 0.4%, the S&P 500 declined 0.34%, and the Nasdaq slid 0.3%.
Watch: 3 Things to Watch in Janet Yellen and Mario Draghi's Jackson Hole Speeches
Uber said it posted a loss of $645 million in the second quarter, narrower than the $708 million loss in the first quarter and the $991 million loss in the fourth quarter of fiscal 2016. Revenue was $1.75 billion, up from $1.5 billion in the first quarter and about $800 million during the same period a year earlier. Gross bookings, or total money collected by fares, jumped to $8.7 billion.
Uber has $6.6 billion cash on hand, compared to about $7.2 billion in the first quarter.
Sears Holdings Corp. (SHLD) reported a second-quarter adjusted loss of $1.16 a share vs. a year-earlier loss of $2.03. Sales were $4.37 billion compared with $5.66 billion in the same period last year.
Sears said Thursday it was still exploring opportunities for its Kenmore and DieHard brands. It also said it would close 28 Kmart stores later in 2017.
Earnings reports are also expected Thursday from Abercrombie & Fitch Co. (ANF - Get Report) , Broadcom Ltd. (AVGO - Get Report) , Staples Inc. (SPLS) , Perry Ellis International Inc. (PERY) , GameStop Corp. (GME - Get Report) , JM Smucker Co. (SJM - Get Report) , VMware Inc. (VMW - Get Report) , Marvell Technology Group Ltd. (MRVL - Get Report) and Brocade Communications Systems Inc. (BRCD) .
Toshiba, the Japanese conglomerate, has been trying to sell its its memory chip business to cover losses from its U.S. nuclear business.
Bosworth will oversee Building 8 and Oculus, Facebook's virtual reality arm, according to Business Insider. The announcement was recently made inside the company by Facebook's chief technical officer, Mike Schroepfer, and a spokesperson confirmed the news to Business Insider.
Bosworth has been at Facebook for more than a decade and was instrumental in helping to create News Feed and Messenger, according to Business Insider. He's also a close confidant to CEO Mark Zuckerberg.
5. -- A single winning Powerball ticket matching all six numbers was sold in Massachusetts.
Powerball Product Group Chair Charlie McIntyre told the Associated Press that the $758.7 million jackpot claimed by a ticket sold in Massachusetts was the largest grand prize won by a single lottery ticket in U.S. history. The ticket was sold at the Handy Variety convenience store in Watertown.---
McIntyre also said six other tickets won $2 million apiece, and 34 more won $1 million.
The lucky numbers: 6, 7, 16, 23 and 26, and a Powerball number of 4.
Watch: 5 Biggest Powerball Prizes in History
Updated from 6:07 a.m. ET
More of What's Trending on TheStreet: