I was very surprised indeed that my little bank accounts used to manage hundreds of euros were also suitable to manage millions, one I sold shares in a startup. I thought I would be called by a full chain of managers and have to present 3D fingerprints of my eyes, then be called by various countries’ TRACFIN and IRS where I used to live. In reality, the French IRS guy told me my declaration was very simple and unsurprising.
1. From the bank's investment arm asking if there were any investment needs I had.
2. From the bank's private banking division to inform me of their services.
I honestly wonder what it takes to get flagged by regulators at this point.
There's even a picture of the check on MS's Twitter: https://twitter.com/morganstanley/status/1315673245291614208...
While it is lot of one person to control individually, and even sizeable for a company to operate daily it is not that much in the grand scheme of things. These days some companies have cash balances that size, famously Apple had more than $200+ Billion in short term assets at one point.
Big banks regularly deal with billions of dollars transferred around everyday. Market makers and central bankers etc do these numbers frequently without blinking twice.
[1] His bankers who are already underwriting the loans can also easily loan him the rest against Tesla stock.