What you need to know on Wall Street right now

Welcome to Finance Insider, Business Insider's summary of the top stories of the past 24 hours.

There has been a lot of news in the investment world in the past 24 hours, so let's dive right in:

• Warren Buffett is investing billions into an industry he once called a "death trap"
• SoftBank is buying Fortress for $3.3 billion
• Billionaire investor Nelson Peltz took a huge stake in Procter & Gamble
• GM's management is facing a nightmare scenario with David Einhorn
• David Einhorn dumped all $143.5 million of his Michael Kors investment
• David Tepper's Appaloosa dropped about $1 billion on 4 pharma stocks
• Billionaire Chase Coleman's Tiger Global made a nearly $500 million bet on Fiat
• Izzy Englander's $35 billion hedge fund made a big bet on Target
• A $20 billion investment firm dumped its huge trade in Apple - and bet on Alphabet and Microsoft
• A $14 billion hedge fund is sounding the alarm on distress in the retail sector
• Morgan Stanley's global head of stock trading just quit to join a $35 billion hedge fund
• Morgan Stanley's top US equity strategist is leaving the bank for a quant shop
• A big Massachusetts pension has yanked its money from one of the hedge fund industry's struggling titans
• Warren Buffett just dropped Walmart and signaled the death of retail as we know it

In bank news, Goldman Sachs just announced a big promotion in its new online business, and is investing $95 million in ad firm MDC Partners.

Fed Chair Janet Yellen is in front of the House Financial Services Committee on Wednesday for the second day of her semiannual Humphrey-Hawkins testimony. Here are the headlines:

• Fed's Yellen speaks out against Trump's Wall Street deregulation push
• Yellen wants to leave the Fed's balance sheet alone for now
• Asked about Trump's immigration plans, Janet Yellen says "slowing immigration would slow economic growth"

There is a bunch of news in the healthcare sector, too. Here's what you need to know:

• The Trump administration just proposed massive changes to Obamacare
• One of the US's largest health-insurance companies is dumping Obamacare; Trump says law "continues to fail"
• Cigna is suing Anthem for $13 billion after walking away from their merger
• AETNA CEO: The Obamacare exchanges are in a "death spiral"

Lastly, here are the 22 best universities outside the developed world.

Here are the top Wall Street headlines from the past 24 hour

One of Wall Street's top equity analysts reveals his biggest fear for 2017 - Business Insider asked the Head of US equity strategy at JP Morgan what keeps him up at night. His answer was loud and clear: An ongoing trend of US dollar strength.

Verizon is reportedly close to a revised deal that cuts Yahoo's price by about $250 million - Verizon has tentatively reached a revised deal with Yahoo, according to Bloomberg.

Twitter CEO Jack Dorsey bought $7 million in stock after its value dropped dramatically - Twitter's stock price dropped 10% last week - and CEO Jack Dorsey is taking the opportunity to hoover up $7 million (£5.6 million) in shares.

Groupon is soaring after its revenue beat - Groupon is up after reporting fourth-quarter earnings on Wednesday morning.

DEUTSCHE BANK: Chinese lending exploded in January - Domestic lending in China shot up in January in a sign the country's credit boom is still accelerating.

Retail sales destroy expectations as gasoline sales soar - US retail sales came in well ahead of expectations for the month of January, according to new data from the Commerce Department.

The ruble dives after Trump tweets 'Was Obama too soft on Russia?' - The Russian ruble extended its earlier losses after President Donald Trump tweeted about President Barack Obama's stance on Russia with respect to Crimea.

28-year-old cofounder of liquor delivery platform shares his advice for aspiring entrepreneurs - Maxim Razmakhin has always been an entrepreneurial spirit. When he was in college, he sold milkshakes out of his dorm room.

Here are the 10 best markets to be a homebuyer - Housing markets in the eastern part of the US continue to lag those out west.