Other Comprehensive Income - Accumulated Other Comprehensive Loss (Income) (Detail) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014		Jun. 30, 2015	Jun. 30, 2014		Dec. 31, 2014
Other Comprehensive Income Loss [Line Items]
Unrealized gain on cash flow hedges, Gross		$ 4.0	$ 0.1		$ 4.3	$ 0.0
Reclassification from AOCI to net income, Gross	[1]	0.3	0.1		0.7	0.5
Gain on cash flow hedges, Gross		4.3	0.2		5.0	0.5
Amortization of unrecognized benefit costs, Gross	[2]	1.6	0.8		2.5	1.6
Decrease (increase) in unrecognized postemployment costs, Gross	[3]		0.0			(12.9)
Total other comprehensive income (loss), Gross		5.9	1.0		7.5	(10.8)
Unrealized gain on cash flow hedges, Tax		(1.4)	0.0		(1.5)	0.0
Reclassification from AOCI to net income, Tax	[1]	(0.1)	(0.1)		(0.4)	(0.2)
Gain on cash flow hedges, Tax		(1.5)	(0.1)		(1.9)	(0.2)
Amortization of unrecognized benefit costs, Tax	[2]	(0.6)	(0.3)		(0.9)	(0.6)
Decrease (increase) in unrecognized postemployment costs, Tax	[3]		0.0			4.7
Total other comprehensive income (loss), Tax		(2.1)	(0.4)		(2.8)	3.9
Unrealized gain on cash flow hedges, Net		2.6	0.1		2.8	0.0
Reclassification from AOCI to net income, Net	[1]	0.2	0.0		0.3	0.3
Gain on cash flow hedges, Net		2.8	0.1		3.1	0.3
Amortization of unrecognized benefit costs, Net	[2]	1.0	0.5		1.6	1.0
Increase in unrecognized postemployment costs		0.0	0.0	[3]	0.0	(8.2)	[3]
Other comprehensive income (loss), net of tax		3.8	0.6		4.7	(6.9)
Unamortized pension loss and prior service credit	[4]	(21.0)			(21.0)			$ (22.5)
Unamortized other benefit gains, prior service costs and transition obligations	[5]	14.0			14.0			13.9
Net unrealized gains (losses) from cash flow hedges	[6]	(4.0)			(4.0)			(7.1)
Total accumulated other comprehensive loss		(11.0)			(11.0)			(15.7)
Tampa Electric Company [Member]
Other Comprehensive Income Loss [Line Items]
Unrealized gain on cash flow hedges, Gross		4.0	0.0		4.3	0.0
Reclassification from AOCI to net income, Gross		0.3	0.0		0.7	0.4
Gain on cash flow hedges, Gross		4.3	0.0		5.0	0.4
Total other comprehensive income (loss), Gross		4.3	0.0		5.0	0.4
Unrealized gain on cash flow hedges, Tax		(1.4)	0.0		(1.5)	0.0
Reclassification from AOCI to net income, Tax		(0.1)	0.0		(0.4)	(0.2)
Gain on cash flow hedges, Tax		(1.5)	0.0		(1.9)	(0.2)
Total other comprehensive income (loss), Tax		(1.5)	0.0		(1.9)	(0.2)
Unrealized gain on cash flow hedges, Net		2.6	0.0		2.8	0.0
Reclassification from AOCI to net income, Net		0.2	0.0		0.3	0.2
Gain on cash flow hedges, Net		2.8	0.0		3.1	0.2
Other comprehensive income (loss), net of tax		2.8	$ 0.0		3.1	$ 0.2
Net unrealized gains (losses) from cash flow hedges	[6]	(4.0)			(4.0)			(7.1)
Total accumulated other comprehensive loss		$ (4.0)			$ (4.0)			$ (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 $12.9 million and $13.8 million as of June 30, 2015 and Dec. 31, 2014, respectively.

[5] Net of tax expense of $8.3 million and $8.3 million as of June 30, 2015 and Dec. 31, 2014, respectively. Balance includes a $7.7 million loss as of June 30, 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.

[6] Net of tax benefit of $2.5 million and $4.5 million as of June 30, 2015 and Dec. 31, 2014, respectively.