interest rate cash flow hedges 2013 we report changes in the fair value of cash flow hedges in accumulated other comprehensive loss until the hedged item affects earnings .at both december 31 , 2008 and 2007 , we had reductions of $ 4 million recorded as an accumulated other comprehensive loss that is being amortized on a straight-line basis through september 30 , 2014 .as of december 31 , 2008 and 2007 , we had no interest rate cash flow hedges outstanding .earnings impact 2013 our use of derivative financial instruments had the following impact on pre-tax income for the years ended december 31 : millions of dollars 2008 2007 2006 .
[['millions of dollars', '2008', '2007', '2006'], ['( increase ) /decrease in interest expense from interest rate hedging', '$ 1', '$ -8 ( 8 )', '$ -8 ( 8 )'], ['( increase ) /decrease in fuel expense from fuel derivatives', '1', '-1 ( 1 )', '3'], ['increase/ ( decrease ) in pre-tax income', '$ 2', '$ -9 ( 9 )', '$ -5 ( 5 )']]
fair value of debt instruments 2013 the fair value of our short- and long-term debt was estimated using quoted market prices , where available , or current borrowing rates .at december 31 , 2008 , the fair value of total debt is approximately $ 247 million less than the carrying value .at december 31 , 2007 , the fair value of total debt exceeded the carrying value by approximately $ 96 million .at december 31 , 2008 and 2007 , approximately $ 320 million and $ 181 million , respectively , of fixed-rate debt securities contained call provisions that allowed us to retire the debt instruments prior to final maturity , with the payment of fixed call premiums , or in certain cases , at par .sale of receivables 2013 the railroad transfers most of its accounts receivable to union pacific receivables , inc .( upri ) , a bankruptcy-remote subsidiary , as part of a sale of receivables facility .upri sells , without recourse on a 364-day revolving basis , an undivided interest in such accounts receivable to investors .the total capacity to sell undivided interests to investors under the facility was $ 700 million and $ 600 million at december 31 , 2008 and 2007 , respectively .the value of the outstanding undivided interest held by investors under the facility was $ 584 million and $ 600 million at december 31 , 2008 and 2007 , respectively .upri reduced the outstanding undivided interest held by investors due to a decrease in available receivables at december 31 , 2008 .the value of the outstanding undivided interest held by investors is not included in our consolidated financial statements .the value of the undivided interest held by investors was supported by $ 1015 million and $ 1071 million of accounts receivable held by upri at december 31 , 2008 and 2007 , respectively .at december 31 , 2008 and 2007 , the value of the interest retained by upri was $ 431 million and $ 471 million , respectively .this retained interest is included in accounts receivable in our consolidated financial statements .the interest sold to investors is sold at carrying value , which approximates fair value , and there is no gain or loss recognized from the transaction .the value of the outstanding undivided interest held by investors could fluctuate based upon the availability of eligible receivables and is directly affected by changing business volumes and credit risks , including default and dilution .if default or dilution percentages were to increase one percentage point , the amount of eligible receivables would decrease by $ 6 million .should our credit rating fall below investment grade , the value of the outstanding undivided interest held by investors would be reduced , and , in certain cases , the investors would have the right to discontinue the facility .the railroad services the sold receivables ; however , the railroad does not recognize any servicing asset or liability as the servicing fees adequately compensate us for these responsibilities .the railroad collected approximately $ 17.8 billion and $ 16.1 billion during the years ended december 31 , 2008 and 2007 , respectively .upri used certain of these proceeds to purchase new receivables under the facility. .

Question: what was the difference in billions of sold receivables from 2007 to 2008?
Answer: 1.7