The government estimates that figure could top $259 billion to support the companies through 2014 after subtracting dividend payments. Fannie has received more than $116 billion so far from the Treasury Department, the most expensive bailout of a single company. Fannie officials say losses have increased in recent quarters for two reasons: Some homeowners are paying less interest after refinancing at historically low mortgage rates; others are defaulting on their mortgages. When property values drop, homeowners default, either because they are unable to afford the payments or because they owe more than the property is worth. Because of the guarantees, Fannie and Freddie must pay for the losses. Fannie's October-December loss takes into account $2.6 billion in dividend payments to the government. That compares with a loss of $2.1 billion in the fourth quarter of 2010. The Associated Press contributed to this report.