Variable Interest Entities (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Long-term Contract for Purchase of Electric Power [Line Items]
Purchased power	$ 31.2	$ 43.9	$ 59.4	$ 71.1
Tampa Electric Co [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Purchased power	31.2	43.9	59.4	71.1
Minimum Range [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Multiple PPAs range			117
Minimum Range [Member] | Tampa Electric Co [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Multiple PPAs range			117
Maximum Range [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Multiple PPAs range			370
Maximum Range [Member] | Tampa Electric Co [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Multiple PPAs range			370
Power Purchase Agreements [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Purchased power	10.5	5.9	25.2	13.0
Power Purchase Agreements [Member] | Tampa Electric Co [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Purchased power	10.5	5.9	25.2	13.0
Power Purchase Agreements [Member] | Variable Interest Entity [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Purchased power	20.8	26.2	43.3	42.0
Power Purchase Agreements [Member] | Variable Interest Entity [Member] | Tampa Electric Co [Member]
Long-term Contract for Purchase of Electric Power [Line Items]
Purchased power	$ 20.8	$ 26.2	$ 43.3	$ 42.0