. the average interest rate payable on the 2020 debentures , including the impact of the interest rate swaps , for 2016 and 2015 was 5.43% ( 5.43 % ) and 5.04% ( 5.04 % ) , respectively . floating rate senior notes the floating rate senior notes bear interest at either one or three-month libor , less a spread ranging from 30 to 45 basis points . the average interest rate for 2016 and 2015 was 0.21% ( 0.21 % ) and 0.01% ( 0.01 % ) , respectively