Short-Term Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended				9 Months Ended	12 Months Ended	9 Months Ended						0 Months Ended	9 Months Ended		0 Months Ended				9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Dec. 17, 2013	Jun. 24, 2013	Sep. 30, 2014 NMGC Credit Agreement [Member]	Sep. 30, 2014 Tampa Electric Company [Member]	Dec. 31, 2013 Tampa Electric Company [Member]	Sep. 30, 2014 Tampa Electric Company [Member] 1-year Accounts Receivable Facility [Member]	Feb. 14, 2014 Tampa Electric Company [Member] 1-year Accounts Receivable Facility [Member]	Dec. 31, 2013 Tampa Electric Company [Member] 1-year Accounts Receivable Facility [Member]	Sep. 30, 2014 Tampa Electric Company [Member] Amended Credit Agreement [Member]	Sep. 30, 2014 New Mexico Gas Company [Member]	Dec. 31, 2013 New Mexico Gas Company [Member]	Sep. 02, 2014 New Mexico Gas Company [Member] NMGC Credit Agreement [Member]	Sep. 30, 2014 New Mexico Gas Company [Member] NMGC Credit Agreement [Member]	Dec. 17, 2013 New Mexico Gas Company [Member] NMGC Credit Agreement [Member]	Dec. 17, 2013 New Mexico Gas Company [Member] NMGC Credit Agreement [Member] Letter of Credit	Sep. 30, 2014 TECO Finance [Member]	Dec. 31, 2013 TECO Finance [Member]	Sep. 30, 2014 TECO Finance [Member] Amended Credit Agreement [Member]	Sep. 30, 2014 Minimum [Member] Tampa Electric Company [Member]	Sep. 30, 2014 Maximum [Member] Tampa Electric Company [Member]
Line Of Credit Facility [Line Items]
Commitment fees, percentage								0.70%													0.125%	0.30%
Weighted-average interest rate							0.56%					1.37%	0.56%					1.37%	0.56%
Amended credit facility	$ 900.0	$ 675.0	$ 40.0		$ 125.0	$ 475.0	$ 475.0	$ 150.0	$ 150.0	$ 150.0	$ 325.0					$ 125.0		$ 200.0		$ 300.0
Debt instrument maturity date						2015-02-13		2015-02-13
Basis spread on federal funds rate								0.50%							0.50%
Credit Facility Amendment Date								Feb. 14, 2014
Line Of Credit Facility Maximum Borrowing Capacity	900.0	675.0	40.0		125.0	475.0	475.0	150.0	150.0	150.0	325.0					125.0		200.0		300.0
Credit facility maturity date	Dec. 17, 2018	Dec. 17, 2018				Dec. 17, 2018	Dec. 17, 2018								Dec. 17, 2018
Interest rate description														as an alternative to the above interest rate, allows NMGC to borrow funds at an interest rate equal to a margin plus the higher of JPMorgan Chase Bank’s prime rate, the federal funds rate plus 50 basis points, or the London interbank deposit rate plus 1.00%;
Increase of credit facility																	75
Senior unsecured bridge credit				1,075
Outstanding borrowings						$ 0