Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2011		Dec. 31, 2010
Unrecognized pension losses and prior service costs	$ (25.5)	[1]	$ (26.6)	[1]
Unrecognized other benefit gains, prior service costs and transition obligations	13.7	[2]	13.6	[2]
Net unrealized losses from cash flow hedges	(5.1)	[3]	(4.2)	[3]
Accumulated Other Comprehensive Income (Loss)	(16.9)		(17.2)
Unrecognized pension losses and prior service costs, tax benefit	15.7		16.2
Unrecognized other benefit gains, prior service costs and transition obligations, tax expense	5.9		5.8
Net unrealized losses from cash flow hedges, tax benefit	3.3		2.7
Tampa Electric Co [Member]
Net unrealized losses from cash flow hedges	(4.8)	[4]	(5.3)	[4]
Accumulated Other Comprehensive Income (Loss)	(4.8)		(5.3)
Net unrealized losses from cash flow hedges, tax benefit	$ 3.0		$ 3.4

[1] Net of tax benefit of $15.7 million and $16.2 million as of Sep. 30, 2011 and Dec. 31, 2010, respectively.

[2] Net of tax expense of $5.9 million and $5.8 million as of Sep. 30, 2011 and Dec. 31, 2010, respectively.

[3] Net of tax benefit of $3.3 million and $2.7 million as of Sep. 30, 2011 and Dec. 31, 2010, respectively.

[4] Net of tax benefit of $3.0 million and $3.4 million as of Sep. 30, 2011 and Dec. 31, 2010, respectively.