facility that would have matured on September 14, 2018. Up to $150 million under this credit facility is available for swingline loans.
Both credit agreements include various covenants, including, among others, maintaining a total debt to total capital leverage ratio of no more than 0.65 to 1.0. At December 31, 2018, we were in compliance with the covenants. These revolving credit facilities are maintained primarily to provide backup liquidity for our commercial paper borrowings and for general corporate purposes. There were no outstanding borrowings under these facilities at December 31, 2018. We intend to maintain credit facilities of a similar aggregate amount by renewing or replacing these facilities before expiration.
At December 31, 2018, we had $780 million of commercial paper outstanding, which effectively reduced the $3.5 billion available capacity under our revolving credit facilities to $2.72 billion.
At December 31, 2018, we also had $237 million available for borrowings under our international and other domestic credit facilities.
Senior notes, 3.65%, due 2023
Debentures, 6.75%, due 2027
Debentures, 7.125%, due 2028
Senior notes, 4.875%, due 2043
Debentures, 5.65%, due 2098 (effective interest rate 7.48%)
Fair value adjustments due to hedge on indebtedness
Total long-term debt
Less: Current maturities of long-term debt
Principal payments required on long-term debt during the next five years are as follows:
Interest on the $500 million aggregate principal amount of 3.65% senior unsecured notes due in 2023 and the $500 million aggregate principal amount of 4.875% senior unsecured notes due in 2043 pay interest semi-annually on April 1 and October 1 of each year.
Interest on the 6.75% debentures is payable on February 15 and August 15 of each year.
Interest on the $250 million 7.125% debentures and $165 million 5.65% debentures is payable on March 1 and September 1 of each year. The debentures are unsecured and are not subject to any sinking fund requirements. We can redeem the 7.125% debentures and the 5.65% debentures at any time prior to maturity at the greater of par plus accrued interest or an amount designed to ensure that the debenture holders are not penalized by the early redemption.
Our debt agreements contain several restrictive covenants. The most restrictive of these covenants applies to our revolving credit facility which will upon default, among other things, limit our ability to incur additional debt or issue preferred stock, enter into sale-leaseback transactions, sell or create liens on our assets, make investments and merge or consolidate with any other entity. In addition, we are subject to a maximum debt-to-EBITDA ratio financial covenant. At December 31, 2018, we were in compliance with all of the covenants under our borrowing agreements.