Commitments and Contingencies - Letters of Credit and Guarantees (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Guarantor Obligations [Line Items]
Year of expiration 2014	$ 0
Year of expiration 2015-2018	0.7
Year of expiration After 2018	96.9
Maximum Theoretical Obligation	97.6
Liabilities Recognized at Sep 30, 2014	0.1
TECO Coal [Member] | Fuel Purchase Related [Member]
Guarantor Obligations [Line Items]
Year of expiration 2014	0
Year of expiration 2015-2018	0.7
Year of expiration After 2018	4.0
Maximum Theoretical Obligation	4.7
Liabilities Recognized at Sep 30, 2014	0
Other Subsidiaries [Member] | Fuel Purchase / Energy Management [Member]
Guarantor Obligations [Line Items]
Year of expiration 2014	0
Year of expiration 2015-2018	0
Year of expiration After 2018	92.9
Maximum Theoretical Obligation	92.9
Liabilities Recognized at Sep 30, 2014	0.1
Tampa Electric Company [Member] | Letters Of Credit [Member] |
Guarantor Obligations [Line Items]
Year of expiration 2014	0
Year of expiration 2015-2018	0
Year of expiration After 2018	0.7
Maximum Theoretical Obligation	0.7
Liabilities Recognized at Sep 30, 2014	0.1
New Mexico Gas Company [Member] | Letters Of Credit [Member] |
Guarantor Obligations [Line Items]
Year of expiration 2014	0
Year of expiration 2015-2018	0
Year of expiration After 2018	1.7
Maximum Theoretical Obligation	1.7
Liabilities Recognized at Sep 30, 2014	$ 1.3