system
A chat on subreddit /r/wallstreetbets
human
Same name fidelity uses. I have a fidelity brokerage account and 'cash management' account. It works just like any bank account and it's really nice I can do all my banking at the same place and have no need for a regular bank.  
  
 I think that's what most of brokerages name their 'banking' accounts. 
  
 However I am like 99% sure the funds in my fidelity CMA are FDIC insured.

gpt
Yeah, they cash sweep to FDIC insured banks. Definitely has nothing to do with SIPC.