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 .

<i>Millions of Dollars</i>
<i>2008</i>
<i>2007</i>
<i>2006</i>
(Increase)/decrease in interest expense from interest rate hedging
$1
$(8)
$(8)
(Increase)/decrease in fuel expense from fuel derivatives
1
(1)
3
Increase/(decrease) in pre-tax income
$2
$(9)
$(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: Analyse this data from a financial earnings document. what was the difference in billions of sold receivables from 2007 to 2008?
Choices:
-1.7
0
1.7
17.8
33.9
Correct choice index: 2