Income Taxes - Schedule of Income Tax Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Income tax expense from continuing operations	$ 155.3	$ 138.9	$ 112.6
Total income tax expense	116.7	89.5	108.8
Tampa Electric Company [Member]
Income Taxes [Line Items]
Current income taxes, Federal	38.2	54.8	19.4
Current income taxes, State	8.4	8.9	1.3
Deferred income taxes, Federal	102.9	79.0	99.8
Deferred income taxes, State	14.5	13.5	18.6
Amortization of investment tax credits	1.5	(0.3)	(0.3)
Income tax expense from continuing operations	165.5	155.9	138.8
Continuing Operations [Member]
Income Taxes [Line Items]
Current income taxes, Federal	(0.5)	0.5	2.2
Current income taxes, State	0.0	0.0	0.0
Deferred income taxes, Federal	133.2	111.0	98.8
Deferred income taxes, State	21.1	27.7	11.9
Amortization of investment tax credits	1.5	(0.3)	(0.3)
Income tax expense from continuing operations	155.3	138.9	112.6
Discontinued Operations [Member]
Income Taxes [Line Items]
Current income taxes, Federal	0.0	0.0	0.0
Current income taxes, State	(0.3)	(0.4)	(3.5)
Deferred income taxes, Federal	(34.7)	(44.0)	(0.3)
Deferred income taxes, State	(3.6)	(5.0)	0.0
Income tax expense from discontinued operations	$ (38.6)	$ (49.4)	$ (3.8)