Food for thought if you have any interest in the potential impact of the European situation on US banks. I have no opinion yet on the quantitative significance of this. $518 billion, though, is not prima facie chump change.
At Bloomberg, a report by Yalman Onaran: Selling More CDS on Europe Debt Raises Risk for U.S. Banks.
The best bit: "The banks say their net positions are smaller because they purchase swaps to offset ones they’re selling to other companies."