Long-Term Debt	3 Months Ended
Mar. 31, 2018
Debt Disclosure [Abstract]
Long-Term Debt	7. Long-Term Debt Fair Value of Long-Term Debt At March 31, 2018, TEC’s long-term debt had a carrying amount of $2,164 million and an estimated fair market value of $2,341 million. At December 31, 2017, TEC’s total long-term debt had a carrying amount of $2,164 million and an estimated fair market value of $2,412 million. The fair value of debt securities determined using Level 1 measurements was $55 million at March 31, 2018 and December 31, 2017. The fair value of the remaining debt securities is determined using Level 2 measurements (see Note 12 for information regarding the fair value hierarchy).

Long-Term Debt

3 Months Ended

Mar. 31, 2018

7. Long-Term Debt

Fair Value of Long-Term Debt

At March 31, 2018, TEC’s long-term debt had a carrying amount of $2,164 million and an estimated fair market value of $2,341 million. At December 31, 2017, TEC’s total long-term debt had a carrying amount of $2,164 million and an estimated fair market value of $2,412 million. The fair value of debt securities determined using Level 1 measurements was $55 million at March 31, 2018 and December 31, 2017. The fair value of the remaining debt securities is determined using Level 2 measurements (see Note 12 for information regarding the fair value hierarchy).