There is relatively little money compared to debt in the financial system. When the debt prices collapse, there is not nearly enough money to cover obligations. If Citi's depositors decided they wanted their $1T, debt prices would collapse and the Fed would have to print nearly all that money. $400B of the $525 you list as cash equivalents was already provided by the Fed.
Well duh!
When the debt prices collapse, there is not nearly enough money to cover obligations.
You think debt prices will collapse from here? Let me know what you're shorting to profit from this collapse.