I don't know more than the basics, my thought was if you pocket $2b/year and invest it, you have $13B+ in 10 years (plus your own $28b you've invested that I didn't include). So $40B to whether a storm every 10 years seems reasonable.
I think you are ignoring a lot of factors that come into play when you are managing assets on the scale of 70B$. It is easy to sink 1000$ in a minute into an index fund using Robinhood. It is not as easy when you are talking numbers on this scale.
> Oversimplified napkin math for fun:
We are having fun!
99% in SPY, 1% in 80% SPY Put option should cover your downside.
I think you're going to find the 80% SPY Put option doesn't have liquidity for 700 million$ of options.