that there are no further revisions to stock-based compensation estimates. 

Quantitative and Qualitative Disclosures About Market Risk 

We are exposed to market risk for the effect of interest rate changes, foreign currency fluctuations, and changes in the market values of our investments. Information relating to quantitative and qualitative disclosures about market risk is set forth below and in Item 7 of Part II, “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Liquidity and Capital Resources.” 

Interest Rate Risk 

Our exposure to market risk for changes in interest rates relates primarily to our investment portfolio and our long-term debt. All of our cash equivalent and marketable fixed income securities are designated as available for sale and, accordingly, are presented at fair value on our consolidated balance sheets. We generally invest our excess cash in investment grade short- to intermediate-term fixed income securities and AAA-rated money market funds. Fixed rate securities may have their fair market value adversely affected due to a rise in interest rates, and we may suffer losses in principal if forced to sell securities that have declined in market value due to changes in interest rates. 

At December 31, 2012, we had $3.7 billion of debt, including the current portion, primarily consisting of fixed rate unsecured debt in three tranches: $750 million of 0.65% notes due in 2015; $1.0 billion of 1.20% notes due in 2017; and $1.3 billion of 2.50% notes due in 2022. The fair value of our debt will fluctuate with movements of interest rates, increasing in periods of declining rates of interest and declining in periods of increasing rates of interest. Based upon quoted market prices and Level 2 inputs, the fair value of our debt was $3.7 billion at December 31, 2012. 

Foreign Exchange Risk 

During 2012, net sales from our International segment accounted for 43% of our consolidated revenues. Net sales and related expenses generated from our international websites, as well as those relating to www.amazon.ca (which is included in our North America segment), are denominated in the functional currencies of the corresponding websites and primarily include Euros, British Pounds, Japanese Yen, and Chinese Yuan. The functional currency of our subsidiaries that either operate or support these websites is the same as the corresponding local currency. The results of operations of, and certain of our intercompany balances associated with, our internationally-focused websites are exposed to foreign exchange rate fluctuations. Upon consolidation, as exchange rates vary, net sales and other operating results may differ materially from expectations, and we may record significant gains or losses on the remeasurement of intercompany balances. For example, as a result of fluctuations in foreign exchange rates during 2012, International segment revenues decreased $853 million in comparison with the prior year. 

We have foreign exchange risk related to foreign-denominated cash, cash equivalents, and marketable securities (“foreign funds”). Based on the balance of foreign funds at December 31, 2012 of $5.1