At December 31, 2020, we carried a total debt balance (including accrued interest) of €5,417.9 million, of which €1,358.0 million principal amount is related to the € and USD-denominated Senior Secured Fixed Rate Notes due March 2028 and €2,987.2 million principal amount is owed under our 2020 Amended Senior Credit Facility with maturities ranging from April 2028 through April 2029. Our total debt balance at December 31, 2020 also included a principal amount of €351.0 million related to our vendor financing program, while the remainder primarily represents lease obligations associated with the Interkabel Acquisition and other leases.
At December 31, 2020, we carried €351.0 million of short-term debt related to our vendor financing program, all of which is maturing within less than twelve months. This represented a modest decrease of €3.9 million versus December 31, 2019 and impacted our Adjusted Free Cash Flow by the same amount. In Q4 2020, the outstanding commitments under our vendor financing program showed an anticipated increase relative to the preceding quarter with an increase of €10.7 million. As of end-October 2020, the applicable margin on our future short-dated commitments under the vendor financing program has been reduced by another 15 basis points to 1.95% over EURIBOR floored at 0%. This reduced interest cost comes on top of an equivalent 15 basis points margin reduction in February 2020. Given the aforementioned size of the program, this will have a modest accretive impact on our Adjusted Free Cash Flow in 2021 and beyond.
In the first half of 2020, we finalized several accretive (re)financing transactions including (i) the successful issuance of a new 8.25-year USD 2,295 million Term Loan (“Facility AR”) and a new 9.25-year €1,110 million Term Loan (“Facility AQ”) in January 2020, (ii) the issuance of a new 6.2-year €510.0 million revolving credit facility in April 2020 ("Revolving Credit Facility I") and (iii) the April 2020 10% repurchase of our 3.50% €600.0 million Senior Secured Fixed Rate Notes due March 2028. In Q4 2020, we successfully extended our €20.0 million bilateral Revolving Credit Facility by another five years to September 30, 2026. The applicable margin under the extended facility has been determined at 2.25% over EURIBOR (floored at 0%), representing the same margin as under our €510.0 million Revolving Credit Facility I which also matures in 2026. The extended facility can customarily be used for general corporate purposes.
Excluding short-term liabilities related to our vendor financing program, we face no debt maturities prior to March 2028 with a weighted average maturity of approximately 7.5 years at December 31, 2020. In addition, we also had full access to €555.0 million of undrawn commitments under our revolving credit facilities at December 31, 2020, with certain availabilities up to September 2026.
For more information on our debt instruments and payment schedule at December 31, 2020, we refer to the Q4 2020 Investor & Analyst Toolkit.