Other Comprehensive Income - Accumulated Other Comprehensive Loss (Income) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Other Comprehensive Income Loss [Line Items]
Unrealized gain on cash flow hedges, Gross		$ 0.0	$ 0.3
Reclassification from AOCI to net income, Gross	[1]	0.3	0.4
Gain on cash flow hedges, Gross		0.3	0.7
Amortization of unrecognized benefit costs, Gross	[2]	0.8	0.9
Total other comprehensive income (loss), Gross		1.1	1.6
Unrealized gain on cash flow hedges, Tax		0.0	(0.2)
Reclassification from AOCI to net income, Tax	[1]	(0.1)	(0.2)
Gain on cash flow hedges, Tax		(0.1)	(0.4)
Amortization of unrecognized benefit costs, Tax	[2]	(0.3)	(0.3)
Total other comprehensive income (loss), Tax		(0.4)	(0.7)
Unrealized gain on cash flow hedges, Net		0.0	0.1
Reclassification from AOCI to net income, Net	[1]	0.2	0.2
Gain on cash flow hedges, Net		0.2	0.3
Amortization of unrecognized benefit costs, Net	[2]	0.5	0.6
Other comprehensive income, net of tax		0.7	0.9
Unamortized pension loss and prior service credit	[3]	(33.6)		$ (34.2)
Unamortized other benefit gains, prior service costs and transition obligations	[4]	25.5		25.6
Net unrealized losses from cash flow hedges	[5]	(3.4)		(3.6)
Total accumulated other comprehensive loss		(11.5)		(12.2)
Tampa Electric Company [Member]
Other Comprehensive Income Loss [Line Items]
Unrealized gain on cash flow hedges, Gross		0.0	0.3
Reclassification from AOCI to net income, Gross		0.3	0.4
Gain on cash flow hedges, Gross		0.3	0.7
Total other comprehensive income (loss), Gross		0.3	0.7
Unrealized gain on cash flow hedges, Tax		0.0	(0.2)
Reclassification from AOCI to net income, Tax		(0.1)	(0.2)
Gain on cash flow hedges, Tax		(0.1)	(0.4)
Total other comprehensive income (loss), Tax		(0.1)	(0.4)
Unrealized gain on cash flow hedges, Net		0.0	0.1
Reclassification from AOCI to net income, Net		0.2	0.2
Gain on cash flow hedges, Net		0.2	0.3
Other comprehensive income, net of tax		0.2	$ 0.3
Net unrealized losses from cash flow hedges	[5]	(3.4)		(3.6)
Total accumulated other comprehensive loss		$ (3.4)		$ (3.6)

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

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

[3] Net of tax benefit of $21.1 million and $21.5 million as of Mar. 31, 2016 and Dec. 31, 2015, respectively.

[4] Net of tax expense of $16.0 million and $16.1 million as of Mar. 31, 2016 and Dec. 31, 2015, respectively.

[5] Net of tax benefit of $2.1 million and $2.3 million as of Mar. 31, 2016 and Dec. 31, 2015, respectively.