Commitments and Contingencies - Letter of Credit and Guarantees (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Product Liability Contingency [Line Items]
2013	$ 0
2014-2017	14.8
After 2017	100.7
Total	115.5
Liabilities Recognized at Dec. 31, 2012	7.2
2013	0
2014-2017	14.8
After 2017	100.7
Total	115.5
Liabilities Recognized at Dec. 31, 2012	7.2
TECO Coal [Member] | Letters of Credit [Member]
Product Liability Contingency [Line Items]
2013	0
2014-2017	0
After 2017	5.4
Total	5.4
Liabilities Recognized at Dec. 31, 2012	1.5
2013	0
2014-2017	0
After 2017	5.4
Total	5.4
Liabilities Recognized at Dec. 31, 2012	1.5
TECO Coal [Member] | Guarantees for Benefit of Fuel purchase related [Member]
Product Liability Contingency [Line Items]
2013	0
2014-2017	4.8
After 2017	0
Total	4.8
Liabilities Recognized at Dec. 31, 2012	4.8
2013	0
2014-2017	4.8
After 2017	0
Total	4.8
Liabilities Recognized at Dec. 31, 2012	4.8
Other subsidiaries [Member] | Fuel purchase/energy management [Member]
Product Liability Contingency [Line Items]
2013	0
2014-2017	10.0
After 2017	95.3
Total	105.3
Liabilities Recognized at Dec. 31, 2012	0.9
2013	0
2014-2017	10.0
After 2017	95.3
Total	105.3
Liabilities Recognized at Dec. 31, 2012	0.9
TAMPA ELECTRIC CO [Member] | Letters of Credit [Member]
Product Liability Contingency [Line Items]
2013	0.8
2014-2017	0
After 2017	0.7
Total	1.5
Liabilities Recognized at Dec. 31, 2012	0.3
2013	0.8
2014-2017	0
After 2017	0.7
Total	1.5
Liabilities Recognized at Dec. 31, 2012	$ 0.3