Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Variable Interest Entity [Line Items]
Purchased power	$ 32.1	$ 45.2	$ 103.2	$ 151.5
Tampa Electric Co [Member] | Variable Interest Entity [Member] | Power Purchase Agreements [Member]
Variable Interest Entity [Line Items]
Purchased power	22.9	29.7	64.9	90.6
Tampa Electric Co [Member] | Power Purchase Agreements [Member]
Variable Interest Entity [Line Items]
Purchased power	12.0	14.7	24.9	45.0
Tampa Electric Co [Member] | Maximum Range[Member]
Variable Interest Entity [Line Items]
Multiple PPAs range			370
Tampa Electric Co [Member] | Minimum Range[Member]
Variable Interest Entity [Line Items]
Multiple PPAs range			121
Tampa Electric Co [Member]
Variable Interest Entity [Line Items]
Purchased power	$ 32.1	$ 45.2	$ 103.2	$ 151.5