What you need to know on Wall Street right now

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

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"

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.