20%

No, not my standard broker's commission, but the average level of credit enhancement in CMBS before 2003. FT alphaville, commenting on the forthcoming tsunami of CMBS downgrades, reprints this enlightening table from S&P:This very clearly shows how investors let their standards slip in the hurt for yield during the Boom years. Not everyone was convinced though: from 2004 the practice of splitting the AAA into two or more tranches became commonplace. The top tranche, amusingly, is called super duper AAA.

S&P want at least 19% credit enhancement for AAA going forward. At least this is generating a nice repack business as banks take junior AAAs and resecuritise to keep most of the notional at AAA. The Americans call this a Re-Remic* -- which isn't nearly as cool sounding as super duper AAA.

* Real estate mortgage investment conduit, or CDO-squared to its friends.