Employee Postretirement Benefits - Schedule of Change in Benefit Obligation (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits [Member]
Change in benefit obligation
Net benefit obligation at beginning of year	$ 715.0	$ 646.4
Service cost	18.2	17.0	16.0
Interest cost	28.9	30.1	30.9
Plan participants' contributions	0	0
Plan amendments	0	0
Actuarial loss (gain)	(50.4)	54.7
Gross benefits paid	(43.1)	(33.2)
Settlements	(2.6)	0
Federal subsidy on benefits paid
Net benefit obligation at end of year	666.0	715.0	646.4
Other Postretirement Benefits [Member]
Change in benefit obligation
Net benefit obligation at beginning of year	230.3	216.5
Service cost	2.5	2.4	2.1
Interest cost	9.3	10.1	11.1
Plan participants' contributions	2.9	3.7
Plan amendments	0	(5.2)
Actuarial loss (gain)	(22.1)	16.3
Gross benefits paid	(15.0)	(14.5)
Settlements	0	0
Federal subsidy on benefits paid	0.2	1.0
Net benefit obligation at end of year	208.1	230.3	216.5
TECO Energy [Member] | Pension Benefits [Member]
Change in benefit obligation
Net benefit obligation at beginning of year	715.0	646.4
Service cost	18.2	17.0	16.0
Interest cost	28.9	30.1	30.9
Plan participants' contributions	0	0
Plan amendments	0	0
Actuarial loss (gain)	(50.4)	54.7
Gross benefits paid	(43.1)	(33.2)
Settlements	(2.6)	0
Net benefit obligation at end of year	666.0	715.0	646.4
TECO Energy [Member] | Other Postretirement Benefits [Member]
Change in benefit obligation
Net benefit obligation at beginning of year	230.3	216.5
Service cost	2.5	2.4	2.1
Interest cost	9.3	10.1	11.1
Plan participants' contributions	2.9	3.7
Plan amendments	0	(5.2)
Actuarial loss (gain)	(22.1)	16.3
Gross benefits paid	(15.0)	(14.5)
Settlements	0	0
Federal subsidy on benefits paid	0.2	1.0
Net benefit obligation at end of year	$ 208.1	$ 230.3	$ 216.5