The details of the deal can be summarized as follows:
Banks can swap half of their junk-rated Greek assets 1:1 into AAA-rated 30-year assets with a fixed interest rate of 4,5% (the interest, however, remains "Greek risk").
They can do the same with the other half except that on this swap they must assume a discount "economically equivalent" to 21% of the net present value (NPV). How that discount will be calculated (NPV of what? perhaps even including foregone income?) remains unclear.
If banks were to sell their Greek assets in the secondary market today (if they could be sold in the first place), they would at best receive 50% of the nominal value. Under the above deal, the banks are likely to receive (adjusted for the various elements of the plan) an estimated 85-90% of the nominal value.
Mr. Ackermann announced with a solemn expression on his face that this deal "is very hard for us". After having made this accouncement, he probably retreated to a private meeting with his colleagues and opened champagne bottles!