Employee Postretirement Benefits (Periodic Expense For Pension And Other Postretirement Benefits) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Defined Benefit Plan Disclosure [Line Items]
Settlement cost				$ 1.6
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	4.0	4.0	12.0	12.1
Interest cost on projected benefit obligations	7.7	8.2	23.2	24.9
Expected return on assets	(9.6)	(9.0)	(28.8)	(27.2)
Amortization of transition obligation	0	0	(0.3)	0
Amortization of prior service (benefit) cost	(0.1)	(0.1)	8.4	(0.3)
Amortization of actuarial loss	2.8	3.2	0	9.4
Pension expense			14.5	18.9
Settlement cost			0	1.6
Net pension expense recognized in the TECO Energy Consolidated Condensed Statements of Income	4.8	6.3	14.5	20.5
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.5	0.8	1.6	2.4
Interest cost on projected benefit obligations	2.8	2.8	8.3	8.2
Expected return on assets	0	0	0	0
Amortization of transition obligation	0.5	0.5	1.7	1.7
Amortization of prior service (benefit) cost	0.2	0.2	0.6	0.6
Amortization of actuarial loss	0.1	0	0.1	0
Pension expense			12.3	12.9
Settlement cost			0	0
Net pension expense recognized in the TECO Energy Consolidated Condensed Statements of Income	$ 4.1	$ 4.3	$ 12.3	$ 12.9