Employee Postretirement Benefits - Schedule of Amounts Recognized in Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 139.6	$ 216.5
Accrued benefit costs and other current liabilities	(3.3)	(5.3)
Deferred credits and other liabilities	(69.7)	(180.6)
Accumulated other comprehensive loss (income), pretax	33.1	53.1
Net amount recognized at end of year	99.7	83.7
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	43.2	59.6
Accrued benefit costs and other current liabilities	(13.3)	(13.1)
Deferred credits and other liabilities	(194.8)	(217.2)
Accumulated other comprehensive loss (income), pretax	(24.2)	(17.9)
Net amount recognized at end of year	(189.1)	(188.6)
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	139.6	216.5
Accrued benefit costs and other current liabilities	(3.3)	(5.3)
Deferred credits and other liabilities	(69.7)	(180.6)
Accumulated other comprehensive loss (income), pretax	33.1	53.1
Net amount recognized at end of year	99.7	83.7
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	43.2	59.6
Accrued benefit costs and other current liabilities	(13.3)	(13.1)
Deferred credits and other liabilities	(194.8)	(217.2)
Accumulated other comprehensive loss (income), pretax	(24.2)	(17.9)
Net amount recognized at end of year	$ (189.1)	$ (188.6)