Income Taxes - Schedule of Income Taxes Calculated on Income before Income Taxes and Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Line Items]
Income tax expense at the federal statutory rate of 35%	$ 138.8	$ 120.9	$ 105.5
State income tax, net of federal income tax	13.6	17.0	7.5
Valuation allowance	0.1	0.9	0.0
Other	2.8	0.1	(0.4)
Income tax expense from continuing operations	$ 155.3	$ 138.9	$ 112.6
Income tax expense as a percent of income from continuing operations, before income taxes	39.20%	40.20%	37.40%
Tampa Electric Company [Member]
Schedule Of Income Tax Expense Benefit Continuing Operations Income Tax Reconciliation [Line Items]
Income tax expense at the federal statutory rate of 35%	$ 154.6	$ 145.7	$ 127.5
State income tax, net of federal income tax	14.8	14.5	13.0
Other	(3.9)	(4.3)	(1.7)
Income tax expense from continuing operations	$ 165.5	$ 155.9	$ 138.8
Income tax expense as a percent of income from continuing operations, before income taxes	37.50%	37.50%	38.10%