Other Comprehensive Income - Accumulated Other Comprehensive Loss (Income) (Detail) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2016		Jun. 30, 2015	Jun. 30, 2016		Jun. 30, 2015	Dec. 31, 2015
Other Comprehensive Income Loss [Line Items]
Unrealized gain on cash flow hedges, Gross		$ 0.0		$ 4.0	$ 0.0		$ 4.3
Reclassification from AOCI to net income, Gross	[1]	0.3		0.3	0.7		0.7
Gain on cash flow hedges, Gross		0.3		4.3	0.7		5.0
Amortization of unrecognized benefit costs and other, Gross	[2]	(0.3)		1.6	0.5		2.5
Recognized cost due to curtailment, Gross	[3]	0.1			0.1
Total other comprehensive income (loss), Gross		0.1		5.9	1.3		7.5
Unrealized gain on cash flow hedges, Tax		0.0		(1.4)	0.0		(1.5)
Reclassification from AOCI to net income, Tax	[1]	(0.1)		(0.1)	(0.3)		(0.4)
Gain on cash flow hedges, Tax		(0.1)		(1.5)	(0.3)		(1.9)
Amortization of unrecognized benefit costs and other, Tax	[2]	0.1		(0.6)	(0.2)		(0.9)
Recognized cost due to curtailment, Tax	[3]	0.0			0.0
Total other comprehensive income (loss), Tax		0.0		(2.1)	(0.5)		(2.8)
Unrealized gain on cash flow hedges, Net		0.0		2.6	0.0		2.8
Reclassification from AOCI to net income, Net	[1]	0.2		0.2	0.4		0.3
Gain on cash flow hedges, Net		0.2		2.8	0.4		3.1
Amortization of unrecognized benefit costs and other, Net	[2]	(0.2)		1.0	0.3		1.6
Recognized cost due to curtailment		0.1	[3]	0.0	0.1	[3]	0.0
Other comprehensive income, net of tax		0.1		3.8	0.8		4.7
Unamortized pension loss and prior service credit	[4]	(33.6)			(33.6)			$ (34.2)
Unamortized other benefit gains, prior service costs and transition obligations	[5]	25.4			25.4			25.6
Net unrealized losses from cash flow hedges	[6]	(3.2)			(3.2)			(3.6)
Total accumulated other comprehensive loss		(11.4)			(11.4)			(12.2)
Tampa Electric Company [Member]
Other Comprehensive Income Loss [Line Items]
Unrealized gain on cash flow hedges, Gross		0.0		4.0	0.0		4.3
Reclassification from AOCI to net income, Gross		0.3		0.3	0.7		0.7
Gain on cash flow hedges, Gross		0.3		4.3	0.7		5.0
Total other comprehensive income (loss), Gross		0.3		4.3	0.7		5.0
Unrealized gain on cash flow hedges, Tax		0.0		(1.4)	0.0		(1.5)
Reclassification from AOCI to net income, Tax		(0.1)		(0.1)	(0.3)		(0.4)
Gain on cash flow hedges, Tax		(0.1)		(1.5)	(0.3)		(1.9)
Total other comprehensive income (loss), Tax		(0.1)		(1.5)	(0.3)		(1.9)
Unrealized gain on cash flow hedges, Net		0.0		2.6	0.0		2.8
Reclassification from AOCI to net income, Net		0.2		0.2	0.4		0.3
Gain on cash flow hedges, Net		0.2		2.8	0.4		3.1
Other comprehensive income, net of tax		0.2		$ 2.8	0.4		$ 3.1
Net unrealized losses from cash flow hedges	[7]	(3.2)			(3.2)			(3.6)
Total accumulated other comprehensive loss		$ (3.2)			$ (3.2)			$ (3.6)

[1] Related to interest rate contracts recognized in Interest expense.

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

[3] Related to the estimated curtailment loss for the SERP. See Note 5 for additional information.

[4] Net of tax benefit of $20.9 million and $21.5 million as of June 30, 2016 and Dec. 31, 2015, respectively.

[5] Net of tax expense of $15.8 million and $16.1 million as of June 30, 2016 and Dec. 31, 2015, respectively

[6] Net of tax benefit of $2.0 million and $2.3 million as of June 30, 2016 and Dec. 31, 2015, respectively

[7] Net of tax benefit of $2.0 million and $2.3 million as of June 30, 2016 and Dec. 31, 2015, respectively.