Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred tax liabilities
Property related	$ 1,519.3	$ 1,391.3
Pension	86.6	62.3
Total deferred tax liabilities	1,605.9	1,453.6
Deferred tax assets
Alternative minimum tax credit carryforward	213.5	214.0
Loss and credit carryforwards	637.5	566.7
Other postretirement benefits	69.5	71.5
Other	117.5	159.6
Total deferred tax assets	1,038.0	1,011.8
Valuation allowance	(2.0)	(4.6)
Total deferred tax assets, net of valuation allowance	1,036.0	1,007.2
Total deferred tax liability, net	569.9	446.4
Less: Current portion of deferred tax asset	0.0	(72.8)
Less: Long term portion of deferred tax asset	(0.8)	0.0
Long-term portion of deferred tax liability, net	570.7	519.2
Tampa Electric Company [Member]
Deferred tax liabilities
Property related	1,431.9	1,328.8
Pension and postretirement benefits	92.0	72.5
Pension	71.1	51.8
Total deferred tax liabilities	1,595.0	1,453.1
Deferred tax assets
Loss and credit carryforwards	80.0	77.7
Medical benefits	47.7	51.0
Insurance reserves	27.6	29.0
Pension and postretirement benefits	92.0	72.5
Capitalized energy conservation assistance costs	21.4	20.3
Other	17.5	18.3
Total deferred tax assets	286.2	268.8
Total deferred tax liability, net	1,308.8	1,184.3
Less: Current portion of deferred tax asset	0.0	(24.8)
Long-term portion of deferred tax liability, net	$ 1,308.8	$ 1,209.1