Other Comprehensive Income - Accumulated Other Comprehensive Loss (Income) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross	$ (0.3)		$ 1.1		$ (0.3)		$ 0.7
Reclassification from AOCI to net income, Gross	0.4	[1]	0.1	[1]	0.9	[1]	1.0	[1]
Gain (Loss) on cash flow hedges, Gross	0.1		1.2		0.6		1.7
Amortization of unrecognized benefit costs, Gross	0.4	[2]	1.0	[2]	2.4	[2]	3.2	[2]
Increase in unrecognized postemployment costs, Gross	0	[3]			(12.9)	[3]
Change in benefit obligation due to remeasurement, Gross	(1.1)				(1.1)
Total other comprehensive income (loss), Gross	(0.6)		4.8		(11.0)		7.5
Recognized benefit costs due to settlement, Gross			2.6				2.6
Unrealized gain (loss) on cash flow hedges, Tax	0.1		(0.4)		0.1		(0.3)
Reclassification from AOCI to net income, Tax	(0.1)	[1]	0	[1]	(0.3)	[1]	(0.3)	[1]
Gain (loss) on cash flow hedges, Tax	0		(0.4)		(0.2)		(0.6)
Amortization of unrecognized benefit costs, Tax	(0.2)	[2]	(0.4)	[2]	(0.8)	[2]	(1.2)	[2]
Increase in unrecognized postemployment costs, Tax	0	[3]			4.7	[3]
Change in benefit obligation due to remeasurement, Tax	0.4				0.4
Total other comprehensive income (loss), Tax	0.2		(1.8)		4.1		(2.8)
Recognized benefit costs due to settlement, Tax			(1.0)				(1.0)
Unrealized gain (loss) on cash flow hedges, Net	(0.2)		0.7		(0.2)		0.4
Reclassification from AOCI to net income, Net	0.3	[1]	0.1	[1]	0.6	[1]	0.7	[1]
Gain (loss) on cash flow hedges, Net	0.1		0.8		0.4		1.1
Amortization of unrecognized benefit costs	0.2	[2]	0.6	[2]	1.6	[2]	2.0	[2]
Increase in unrecognized postemployment costs, Net	0	[3]			(8.2)	[3]
Change in benefit obligation due to remeasurement, Net	(0.7)				(0.7)
Other comprehensive income (loss), net of tax	(0.4)		3.0		(6.9)		4.7
Recognized benefit costs due to settlement, Net	0		1.6		0		1.6
Unrecognized pension loss and prior service credit	(19.9)	[4]			(19.9)	[4]			(20.5)	[4]
Unrecognized other benefit loss, prior service cost and transition obligation	7.2	[5]			7.2	[5]			15.1	[5]
Net unrealized losses from cash flow hedges	(7.4)	[6]			(7.4)	[6]			(7.8)	[6]
Total accumulated other comprehensive loss	(20.1)				(20.1)				(13.2)
Tampa Electric Company [Member]
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross	0		0		0		0
Reclassification from AOCI to net income, Gross	0.4		0.4		0.8		1.1
Gain (Loss) on cash flow hedges, Gross	0.4		0.4		0.8		1.1
Total other comprehensive income (loss), Gross	0.4		0.4		0.8		1.1
Unrealized gain (loss) on cash flow hedges, Tax	0		0		0		0
Reclassification from AOCI to net income, Tax	(0.1)		(0.2)		(0.3)		(0.4)
Gain (loss) on cash flow hedges, Tax	(0.1)		(0.2)		(0.3)		(0.4)
Total other comprehensive income (loss), Tax	(0.1)		(0.2)		(0.3)		(0.4)
Unrealized gain (loss) on cash flow hedges, Net	0		0		0		0
Reclassification from AOCI to net income, Net	0.3		0.2		0.5		0.7
Gain (loss) on cash flow hedges, Net	0.3		0.2		0.5		0.7
Other comprehensive income (loss), net of tax	0.3		0.2		0.5		0.7
Net unrealized losses from cash flow hedges	(7.3)	[7]			(7.3)	[7]			(7.8)	[7]
Total accumulated other comprehensive loss	$ (7.3)				$ (7.3)				$ (7.8)

[1] Related to interest rate contracts recognized in Interest expense and commodity contracts recognized in 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 $12.3 million and $12.6 million as of Sept. 30, 2014 and Dec. 31, 2013, respectively.

[5] Net of tax expense of $4.4 million and $9.1 million as of Sept. 30, 2014 and Dec. 31, 2013, respectively. Balance includes a $7.8 million loss 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 18.

[6] Net of tax benefit of $4.7 million and $4.9 million as of Sept. 30, 2014 and Dec. 31, 2013, respectively.

[7] Net of tax benefit of $4.6 million and $4.9 million as of Sept. 30, 2014 and Dec. 31, 2013, respectively.