Commitments and Contingencies - Letters of Credit and Guarantees (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Guarantor Obligations [Line Items]
2013	$ 0
2014-2017	16.3
After 2017	98.3
Total	114.6
Liabilities Recognized at Sep 30, 2013	7.6
TECO Coal [Member] | Guarantees for Benefit of Fuel purchase related [Member]
Guarantor Obligations [Line Items]
2013	0
2014-2017	1.4
After 2017	4.0
Total	5.4
Liabilities Recognized at Sep 30, 2013	2.3
Other Subsidiaries [Member] | Guaranty Under Sale Agreement [Member]
Guarantor Obligations [Line Items]
2013	0
2014-2017	4.9
After 2017	0
Total	4.9
Liabilities Recognized at Sep 30, 2013	4.9
Other Subsidiaries [Member] | Fuel purchase/energy management [Member]
Guarantor Obligations [Line Items]
2013	0
2014-2017	10.0
After 2017	94.3
Total	104.3
Liabilities Recognized at Sep 30, 2013	0.4
Tampa Electric Company [Member] | Letters of Credit [Member]
Guarantor Obligations [Line Items]
2013	0.8
2014-2017	0
After 2017	0.7
Total	1.5
Liabilities Recognized at Sep 30, 2013	$ 0.3