Short-Term Debt - Credit Facilities (Parenthetical) (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Line Of Credit Facility [Line Items]
Credit facility maturity date	Dec. 17, 2018	Dec. 17, 2018
Tampa Electric Company [Member]
Line Of Credit Facility [Line Items]
Credit facility maturity date	Dec. 17, 2018	Dec. 17, 2018