There's no guaranteed interest rate, since the amount of money homeowners collectively pay back every month is a function of how many have refinanced and how many have defaulted.

Many insurers across the continent happily sold policies in the 1980s and 1990s with guaranteed minimum returns in the belief that long-term interest rates would not fall much below 5%.

Nan Shan is burdened with unprofitable guaranteed-return policies it sold in the 1990s when interest rates were higher, raising concerns that a buyer may need to inject more capital.