The counterparty credit risk exposure of 12 US bank holding companies and international banking companies to monoline insurers has led to some $54 billion in write-downs by the banks since 2007. ISDA conducted this study as part of its examination into the losses incurred in the US banking system due to counterparty defaults on OTC derivatives. An earlier paper on the subject (below, dated August 5, 2011), showed such losses for US banks amounted to only $2.7 billion from 2007 through the first quarter of 2011. After further investigation, it became apparent that the transactions involving subprime mortgage risk taken in synthetic form (via derivatives) were booked in firms outside the US banking system.