Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 4.2	$ 4.3	$ 8.3	$ 9.1
Interest cost on projected benefit obligations	8.2	7.2	16.4	14.4
Expected return on assets	(10.4)	(9.5)	(20.7)	(19.2)
Amortization of:
Prior service (benefit) cost	(0.1)	(0.1)	(0.2)	(0.2)
Actuarial loss	3.5	5.3	6.7	10.3
Net pension expense recognized in the TECO Energy Consolidated Condensed Statements of Income	5.4	7.2	10.5	14.4
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.6	0.5	1.2	1.2
Interest cost on projected benefit obligations	2.6	2.4	5.2	4.7
Expected return on assets	0	0	0	0
Amortization of:
Prior service (benefit) cost	(0.1)	(0.1)	(0.1)	(0.2)
Actuarial loss	0.1	0.2	0.1	0.5
Net pension expense recognized in the TECO Energy Consolidated Condensed Statements of Income	$ 3.2	$ 3.0	$ 6.4	$ 6.2