Not sure if this is accurate but I've read he used to sell put options relying on the float from his insurance business as collateral. He could easily be doing

Not sure if this is accurate but I've read he used to sell put options relying on the float from his insurance business as collateral. He could easily be doing this using t-bills as collateral as well. The drops in cash could even partly be explained by having to use that money on puts being exercised.. although I suspect if he is doing this it's probably on a small fraction of that cash.