When the Group transfers financial assets to securitization vehicles, it may retain one or more subordinated tranches, cash reserve accounts, or in some cases, servicing rights or interest-only strips, all of which are retained interests in the securitized assets. The amount of the gain or loss on transfers accounted for as sales depends in part on the previous carrying amounts of the financial assets involved in the transfer, allocated between the assets sold and the retained interests based on their relative fair values at the date of transfer. Retained interests other than servicing rights are classified as trading assets, securities available for sale or other assets depending on the nature of the retained interest and management intent. Servicing rights are classified in intangible assets, carried at the lower of the allocated basis or current fair value and amortized in proportion to and over the period of net servicing revenue.
To obtain fair values, quoted market prices are used if available. However, for securities representing retained interests from securitizations of financial assets, quotes are often not available, so the Group generally estimates fair value based on the present value of future expected cash flows using management's best estimates of the key assumptions (loan losses, prepayment speeds, forward yield curves, and discount rates) commensurate with the risks involved. Interest revenues on retained interests is recognized using the effective yield method.