Long-Term Debt	6 Months Ended
Jun. 30, 2018
Debt Disclosure [Abstract]
Long-Term Debt	7. Long-Term Debt Fair Value of Long-Term Debt At June 30, 2018, TEC’s long-term debt had a carrying amount of $2,205 million and an estimated fair market value of $2,073 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 zero at June 30, 2018 and $55 million at 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). Issuance of Tampa Electric Company 4.3% Notes due 2048 On June 7, 2018, TEC completed an offering of $350 million aggregate principal amount of 4.3% unsecured notes due June 15, 2048 (the TEC 2018 Notes). Until December 15, 2047, TEC may redeem all or any part of the TEC 2018 Notes at its option at any time and from time to time at a redemption price equal to the greater of (i) 100% of the principal amount of the TEC 2018 Notes to be redeemed or (ii) the sum of the present value of the remaining payments of principal and interest on the TEC 2018 Notes to be redeemed, discounted at an applicable treasury rate (as defined in the indenture), plus 20 basis points; in either case, the redemption price would include accrued and unpaid interest to the redemption date. At any time on or after December 15, 2047, TEC may, at its option, redeem the TEC 2018 Notes, in whole or in part, at 100% of the principal amount of the TEC 2018 Notes being redeemed plus accrued and unpaid interest thereon to, but excluding, the date of redemption.

7. Long-Term Debt

Fair Value of Long-Term Debt

At June 30, 2018, TEC’s long-term debt had a carrying amount of $2,205 million and an estimated fair market value of $2,073 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 zero at June 30, 2018 and $55 million at 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).

Issuance of Tampa Electric Company 4.3% Notes due 2048

On June 7, 2018, TEC completed an offering of $350 million aggregate principal amount of 4.3% unsecured notes due June 15, 2048 (the TEC 2018 Notes). Until December 15, 2047, TEC may redeem all or any part of the TEC 2018 Notes at its option at any time and from time to time at a redemption price equal to the greater of (i) 100% of the principal amount of the TEC 2018 Notes to be redeemed or (ii) the sum of the present value of the remaining payments of principal and interest on the TEC 2018 Notes to be redeemed, discounted at an applicable treasury rate (as defined in the indenture), plus 20 basis points; in either case, the redemption price would include accrued and unpaid interest to the redemption date. At any time on or after December 15, 2047, TEC may, at its option, redeem the TEC 2018 Notes, in whole or in part, at 100% of the principal amount of the TEC 2018 Notes being redeemed plus accrued and unpaid interest thereon to, but excluding, the date of redemption.