This excerpt taken from the C 10-Q filed Nov 5, 2007.
Market Value Gains Due to the Change in Citigroup Credit Spreads
SFAS 159 provides companies the ability to elect fair value accounting for many financial assets and liabilities. As part of Citigroup's adoption of this standard in the first quarter of 2007, the Company elected the fair value option on debt instruments that are provided to customers so that this debt and the associated assets the Company purchased to meet this liability are on the same fair value basis in earnings. At the end of the third quarter, $28.6 billion of debt related to customer products was classified as either short- or long-term debt on the Consolidated Balance Sheet.
Under fair value accounting, we are required to use Citigroup credit spreads in determining the market value of any Citigroup liabilities for which the fair value option was elected, as well as for Citigroup trading liabilities such as derivatives. The inclusion of Citigroup credit spreads in valuing Citigroup's liabilities gave rise to a pre-tax gain of $466 million in the third quarter of 2007 and is reflected in the Securities and Banking business.