Other Comprehensive Income - Accumulated Other Comprehensive Loss (Income) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross	$ 0.3		$ (0.1)
Reclassification from AOCI to net income, Gross	0.4	[1]	0.4	[1]
Gain (Loss) on cash flow hedges, Gross	0.7		0.3
Amortization of unrecognized benefit costs, Gross	0.9	[2]	0.8	[2]
Increase in unrecognized postemployment costs, Gross			(12.9)	[3]
Total other comprehensive income (loss), Gross	1.6		(11.8)
Unrealized gain (loss) on cash flow hedges, Tax	(0.2)		0
Reclassification from AOCI to net income, Tax	(0.2)	[1]	(0.1)	[1]
Gain (loss) on cash flow hedges, Tax	(0.4)		(0.1)
Amortization of unrecognized benefit costs, Tax	(0.3)	[2]	(0.3)	[2]
Increase in unrecognized postemployment costs, Tax			4.7	[3]
Total other comprehensive income (loss), Tax	(0.7)		4.3
Unrealized gain (loss) on cash flow hedges, Net	0.1		(0.1)
Reclassification from AOCI to net income, Net	0.2	[1]	0.3	[1]
Gain (loss) on cash flow hedges, Net	0.3		0.2
Amortization of unrecognized benefit costs	0.6	[2]	0.5	[2]
Increase in unrecognized postemployment costs, Net			(8.2)	[3]
Other comprehensive income (loss), net of tax	0.9		(7.5)
Unamortized pension loss and prior service credit	(22.0)	[4]			(22.5)	[4]
Unamortized other benefit gains, prior service costs and transition obligations	14.0	[5]			13.9	[5]
Net unrealized losses from cash flow hedges	(6.8)	[6]			(7.1)	[6]
Total accumulated other comprehensive loss	(14.8)				(15.7)
Tampa Electric Company [Member]
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross	0.3		0
Reclassification from AOCI to net income, Gross	0.4		0.4
Gain (Loss) on cash flow hedges, Gross	0.7		0.4
Total other comprehensive income (loss), Gross	0.7		0.4
Unrealized gain (loss) on cash flow hedges, Tax	(0.2)		0
Reclassification from AOCI to net income, Tax	(0.2)		(0.2)
Gain (loss) on cash flow hedges, Tax	(0.4)		(0.2)
Total other comprehensive income (loss), Tax	(0.4)		(0.2)
Unrealized gain (loss) on cash flow hedges, Net	0.1		0
Reclassification from AOCI to net income, Net	0.2		0.2
Gain (loss) on cash flow hedges, Net	0.3		0.2
Other comprehensive income (loss), net of tax	0.3		0.2
Net unrealized losses from cash flow hedges	(6.8)	[6]			(7.1)	[6]
Total accumulated other comprehensive loss	$ (6.8)				$ (7.1)

[1] Related to interest rate contracts recognized in Interest expense and commodity contracts recognized in Income (loss) from discontinued operations.

[2] Related to postretirement and postemployment benefits. See Note 5 for additional information.

[3] Amounts reflect an out-of-period adjustment related to TECO Coal's unfunded black lung liability.

[4] Net of tax benefit of $13.5 million and $13.8 million as of Mar. 31, 2015 and Dec. 31, 2014, respectively.

[5] Net of tax expense of $8.4 million and $8.3 million as of Mar. 31, 2015 and Dec. 31, 2014, respectively. Balance includes a $7.7 million loss as of Mar. 31, 2015 related to TECO Coal's unfunded black lung liability that will be reclassified from AOCI to net income from discontinued operations upon the settlement of the black lung obligation at the sale date. See Note 15.

[6] Net of tax benefit of $4.1 million and $4.5 million as of Mar. 31, 2015 and Dec. 31, 2014, respectively.