My concerns for the banks - all of them, not just the big ones - is that the derivatives' mountains that they all labour under are too complex to be understood, and that a small variation from normal trading conditions can cause the whole lot to collapse.
That really happened to the NAB. One tiny part of their loan p/f, $17bn, caused them losses of $4.2bn because they got the deris wrong - that was back in the early 2000s. Why do you think the Fed pumped so hard in 2007/8/9/10/11 - to stop it happening on a larger scale. If you can stop liabilities crystallising, you won't be insolvent.
Propping up a seemingly insignificant counterparty can stop a whole house of cards from tumbling.
