and various other factors that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. However, because future events and their effects cannot be determined with certainty, actual results may differ from these assumptions and estimates, and such differences could be material. Critical accounting policies for Equinix that affect our more significant judgment and estimates used in the preparation of our condensed consolidated financial statements include accounting for income taxes, accounting for business combinations, accounting for impairment of goodwill and accounting for property, plant and equipment, which are discussed in more detail under the caption "Critical Accounting Policies and Estimates" in Management's Discussion and Analysis of Financial Condition and Results of Operations, set forth in Part II Item 7, of our Annual Report on Form 10-K for the year ended December 31, 2017.
Recent Accounting Pronouncements
See Note 1 of Notes to Condensed Consolidated Financial Statements in Part I Item 1 of this Quarterly Report on Form 10-Q.
Quantitative and Qualitative Disclosures about Market Risk
There have been no significant changes in our market risk, investment portfolio risk, interest rate risk, foreign currency risk and commodity price risk exposures and procedures during the nine months ended September 30, 2018 as compared to the respective risk exposures and procedures disclosed in Quantitative and Qualitative Disclosures About Market Risk, set forth in Part II Item 7A, of our Annual Report on Form 10-K for the year ended December 31, 2017, other than factors discussed below.
Foreign Currency Risk
To help manage the exposure to foreign currency exchange rate fluctuations, we have implemented a number of hedging programs, in particular (i) a cash flow hedging program to hedge the forecasted revenues and expenses in our EMEA region, (ii) a balance sheet hedging program to hedge the re-measurement of monetary assets and liabilities denominated in foreign currencies, and (iii) a net investment hedging program to hedge the long term investments in our foreign subsidiaries. Our hedging programs reduce, but do not entirely eliminate, the impact of currency exchange rate movements and its impact on the consolidated statements of operations.
We have entered into various foreign currency debt obligations. As of September 30, 2018, the total principal amount of foreign currency debt obligations was $4,553.0 million, including $3,192.2 million denominated in Euro, $635.7 million denominated in British Pound, $418.0 million denominated in Japanese Yen and $307.1 million denominated in Swedish Krona. As of September 30, 2018, we have designated $4,190.8 million of the total principal amount of foreign currency debt obligations as net investment hedges against our net investments in foreign subsidiaries. For a net investment hedge, changes in the fair value of the hedging instrument designated as a net investment hedge, except the ineffective portion and forward points, are recorded as a component of other comprehensive income in the consolidated balance sheets. We did not record any ineffectiveness during the nine months ended September 30, 2018.
Fluctuations in the exchange rates between these foreign currencies (i.e. Euro, British Pound, Swedish Krona and Japanese Yen) and the U.S. Dollar will impact the amount of U.S. dollars that we will require to settle the foreign currency debt obligations at maturity. If the U.S. Dollar would have been weaker or stronger by 10% in comparison to these foreign currencies as of September 30, 2018, we estimate our obligation to cash settle the principal of these foreign currency debt obligations in U.S. dollars would have increased or decreased by approximately $455.3 million respectively.
The U.S. dollar strengthened relative to certain of the currencies of the foreign countries in which we operate during the nine months ended September 30, 2018. This has significantly impacted our condensed consolidated financial position and results of operations during this period, including the amount of revenues that we reported. Continued strengthening or weakening of the U.S. dollar will continue to have a significant impact to us in future periods.
With the existing cash flow hedges in place, a hypothetical additional 10% strengthening of the U.S. dollar for the nine months ended September 30, 2018 would have resulted in a reduction of our revenues and operating expenses including depreciation and amortization expense by approximately $104.4 million and $109.7 million, respectively.
With the existing cash flow hedges in place, a hypothetical additional 10% weakening of the U.S. dollar for the nine months ended September 30, 2018 would have resulted in an increase of our revenues and operating expenses including depreciation and amortization expense by approximately $132.1 million and $134.0 million, respectively.