This excerpt taken from the C 10-Q filed Aug 3, 2007.
Hedging the overall changes in cash flowsIn situations where the contractual rate of a variable rate asset or liability is not a benchmark rate, Citigroup designates the risk of overall changes in cash flows as the hedged risk. Citigroup primarily hedges variability in the total cash flows related to non-benchmark-rate-based liabilities, such as customer deposits with stated maturities, and uses receive-variable, pay-fixed interest rate swaps as the hedging instrument. These cash flow hedging relationships use regression or dollar-offset ratio analysis to assess effectiveness at inception and on an ongoing basis.
Citigroup also hedges the forecasted purchase of mortgage-backed securities and designates the overall change in the purchase price as a hedged risk. The assessment of effectiveness is based on ensuring that the critical terms of the hedging instrument and the hedged item match exactly.