Other Comprehensive Income - Accumulated Other Comprehensive Loss (Income) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross		$ 4.3		$ (0.5)		$ 1.0
Reclassification from AOCI to net income, Gross	[1]	1.4		1.6		1.3
Gain (Loss) on cash flow hedges, Gross		5.7		1.1		2.3
Amortization of unrecognized benefit costs and other, Gross	[2]	3.4		(4.8)		23.6
Increase in unrecognized postemployment costs, Gross	[3]			(12.9)
Change in benefit obligation due to valuation, Gross		(15.5)	[4]	12.6	[5]
Recognized cost due to settlement, Gross		12.1	[6]			2.6
Total other comprehensive income (loss), Gross		5.7		(4.0)		28.5
Unrealized gain (loss) on cash flow hedges, Tax		(1.5)		0.2		(0.4)
Reclassification from AOCI to net income, Tax	[1]	(0.7)		(0.6)		(0.5)
Gain (Loss) on cash flow hedges, Tax		(2.2)		(0.4)		(0.9)
Amortization of unrecognized benefit costs and other, Tax	[2]	(1.3)		1.8		(8.8)
Increase in unrecognized postemployment costs, Tax	[3]			4.7
Change in benefit obligation due to valuation, Tax		5.7	[4]	(4.6)	[5]
Recognized cost due to settlement, Tax		(4.4)	[6]			(1.0)
Total other comprehensive income (loss), Tax		(2.2)		1.5		(10.7)
Unrealized gain (loss) on cash flow hedges, Net		2.8		(0.3)		0.6
Reclassification from AOCI to net income, Net	[1]	0.7		1.0		0.8
Gain (Loss) on cash flow hedges, Net		3.5		0.7		1.4
Amortization of unrecognized benefit costs and other	[2]	2.1		(3.0)		14.8
Increase in unrecognized postemployment costs		0.0		(8.2)	[3]	0.0
Change in benefit obligation due to valuation, Net		(9.8)	[4]	8.0	[5]
Recognized cost due to settlement, Net		7.7	[6]	0.0		1.6
Other comprehensive income (loss), net of tax		3.5		(2.5)		17.8
Unamortized pension losses and prior service credits	[7]	(34.2)		(22.5)
Unamortized other benefit gains, prior service costs and transition obligations	[8]	25.6		13.9
Net unrealized losses from cash flow hedges	[9]	(3.6)		(7.1)
Total accumulated other comprehensive loss		(12.2)		(15.7)
Tampa Electric Company [Member]
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross		4.3		0.0		0.0
Reclassification from AOCI to net income, Gross		1.4		1.1		1.4
Gain (Loss) on cash flow hedges, Gross		5.7		1.1		1.4
Total other comprehensive income (loss), Gross		5.7		1.1		1.4
Unrealized gain (loss) on cash flow hedges, Tax		(1.5)		0.0		0.0
Reclassification from AOCI to net income, Tax		(0.7)		(0.4)		(0.5)
Gain (Loss) on cash flow hedges, Tax		(2.2)		(0.4)		(0.5)
Total other comprehensive income (loss), Tax		(2.2)		(0.4)		(0.5)
Unrealized gain (loss) on cash flow hedges, Net		2.8		0.0		0.0
Reclassification from AOCI to net income, Net		0.7		0.7		0.9
Gain (Loss) on cash flow hedges, Net		3.5		0.7		0.9
Other comprehensive income (loss), net of tax		3.5		0.7		$ 0.9
Net unrealized losses from cash flow hedges	[9]	(3.6)		(7.1)
Total accumulated other comprehensive loss		$ (3.6)		$ (7.1)

[1] Related to interest rate contracts 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] Related to the transfer of employees and their associated postretirement benefits from TEC to TSI, the TECO Energy shared services company. TEC recognized these deferred costs as regulatory assets, whereas TSI recognized them in AOCI.

[5] Includes an adjustment to eliminate TECO Coal’s OPEB liability. See Note 5 for additional information.

[6] Related to the settlement of the TECO Coal black lung obligation at the closing of the sale. See Note 19 for additional information.

[7] Net of tax benefit of $21.5 million and $13.8 million as of Dec. 31, 2015 and 2014, respectively.

[8] Net of tax expense of $16.1 million and $8.3 million as of Dec. 31, 2015 and 2014, respectively. The Dec. 31, 2014 balance included a $7.7 million loss related to TECO Coal’s unfunded black lung liability that was reclassified from AOCI to net income from discontinued operations upon the settlement of the black lung obligation at the sale date. See Note 5.

[9] Net of tax benefit of $2.3 million and $4.5 million as of Dec. 31, 2015 and 2014, respectively.