Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 18.2	$ 17.0	$ 16.0
Interest cost	28.9	30.1	30.9
Expected return on plan assets	(38.4)	(37.1)	(38.4)
Amortization of:
Actuarial loss	20.5	15.3	11.3
Prior service (benefit) cost	(0.4)	(0.4)	(0.4)
Transition obligation	0	0	0
Settlement loss	1.0	0	0.9
Net periodic benefit cost	29.8	24.9	20.3
Prior service cost	0	0	0
Net loss (gain)	(75.7)	34.0	43.3
Amortization of:
Actuarial gain (loss)	(21.5)	(15.3)	(12.2)
Prior service (benefit) cost	0.4	0.4	0.4
Transition obligation	0	0	0
Total recognized in OCI and regulatory assets	(96.8)	19.1	31.5
Total recognized in net periodic benefit cost, OCI and regulatory assets	(67.0)	44.0	51.8
Pension Benefits [Member] | TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	18.2	17.0	16.0
Interest cost	28.9	30.1	30.9
Expected return on plan assets	(38.4)	(37.1)	(38.4)
Amortization of:
Actuarial loss	20.5	15.3	11.3
Prior service (benefit) cost	(0.4)	(0.4)	(0.4)
Transition obligation	0	0	0
Settlement loss	1.0	0	0.9
Net periodic benefit cost	29.8	24.9	20.3
Prior service cost	0	0	0
Net loss (gain)	(75.7)	34.0	43.3
Amortization of:
Actuarial gain (loss)	(21.5)	(15.3)	(12.2)
Prior service (benefit) cost	0.4	0.4	0.4
Transition obligation	0	0	0
Total recognized in OCI and regulatory assets	(96.8)	19.1	31.5
Total recognized in net periodic benefit cost, OCI and regulatory assets	(67.0)	44.0	51.8
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2.5	2.4	2.1
Interest cost	9.3	10.1	11.1
Expected return on plan assets	0	0	0
Amortization of:
Actuarial loss	1.0	0.1	0.1
Prior service (benefit) cost	(0.3)	0.8	0.8
Transition obligation	0	1.8	2.3
Settlement loss	0	0	0
Net periodic benefit cost	12.4	15.2	16.4
Prior service cost	0	(5.2)	0
Net loss (gain)	(15.6)	16.3	(7.4)
Amortization of:
Actuarial gain (loss)	(1.0)	(0.1)	(0.1)
Prior service (benefit) cost	0.3	(0.8)	(0.8)
Transition obligation	0	(1.8)	(2.4)
Total recognized in OCI and regulatory assets	(16.3)	8.4	(10.7)
Total recognized in net periodic benefit cost, OCI and regulatory assets	(3.9)	23.6	5.7
Other Postretirement Benefits [Member] | TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2.5	2.4	2.1
Interest cost	9.3	10.1	11.1
Expected return on plan assets	0	0	0
Amortization of:
Actuarial loss	1.0	0.1	0.1
Prior service (benefit) cost	(0.3)	0.8	0.8
Transition obligation	0	1.8	2.3
Settlement loss	0	0	0
Net periodic benefit cost	12.4	15.2	16.4
Prior service cost	0	(5.2)	0
Net loss (gain)	(15.6)	16.3	(7.4)
Amortization of:
Actuarial gain (loss)	(1.0)	(0.1)	(0.1)
Prior service (benefit) cost	0.3	(0.8)	(0.8)
Transition obligation	0	(1.8)	(2.4)
Total recognized in OCI and regulatory assets	(16.3)	8.4	(10.7)
Total recognized in net periodic benefit cost, OCI and regulatory assets	$ (3.9)	$ 23.6	$ 5.7