Consolidated Statements of Capitalization - Capital Stock (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Preferred stock - par value | $ / shares	$ 100
Preferred stock, no par value | $ / shares
Equity contributions made by TECO Energy | $	$ 190
Preferred Stock Par Value [Member]
Preferred stock, shares authorized	1,500,000
Preferred stock, shares outstanding	0
Preferred Stock No Par Value [Member]
Preferred stock, shares authorized	2,500,000
Preferred stock, shares outstanding	0
Preference Stock No Par Value [Member]
Preferred stock, no par value | $ / shares
Preferred stock, shares authorized	2,500,000
Preferred stock, shares outstanding	0