Commitments and Contingencies - Schedule of Long-term Commitments (Detail) $ in Millions	Dec. 31, 2015 USD ($)
Long Term Commitments [Line Items]
Future Minimum Capacity Payments Under PPAs Due, 2016	$ 14.6
Future Minimum Capacity Payments Under PPAs Due, 2017	9.9
Future Minimum Capacity Payments Under PPAs Due, 2018	10.1
Future Minimum Capacity Payments Under PPAs Due, 2019	0.0
Future Minimum Capacity Payments Under PPAs Due, 2020	0.0
Future Minimum Capacity Payments Under PPAs Due, Thereafter	0.0
Total future minimum capacity payments under PPAs due	34.6
Future Minimum Operating Leases Payments Due, 2016	7.7
Future Minimum Operating Leases Payments Due, 2017	7.1
Future Minimum Operating Leases Payments Due, 2018	6.4
Future Minimum Operating Leases Payments Due, 2019	5.7
Future Minimum Operating Leases Payments Due, 2020	5.4
Future Minimum Operating Leases Payments Due, Thereafter	18.6
Total future minimum operating leases payments due	50.9
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2016	222.5
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2017	21.5
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2018	9.6
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2019	9.7
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2020	4.7
Future Minimum Net Purchase Obligations/Commitments Payments Due, Thereafter	20.0
Total future minimum net purchase obligations/commitments payments due	288.0
Future Minimum Payments Due, 2016	244.8
Future Minimum Payments Due, 2017	38.5
Future Minimum Payments Due, 2018	26.1
Future Minimum Payments Due, 2019	15.4
Future Minimum Payments Due, 2020	10.1
Future Minimum Payments Due, Thereafter	38.6
Total future minimum payments	373.5
Tampa Electric Company [Member]
Long Term Commitments [Line Items]
Future Minimum Capacity Payments Under PPAs Due, 2016	14.6
Future Minimum Capacity Payments Under PPAs Due, 2017	9.9
Future Minimum Capacity Payments Under PPAs Due, 2018	10.1
Future Minimum Capacity Payments Under PPAs Due, 2019	0.0
Future Minimum Capacity Payments Under PPAs Due, 2020	0.0
Future Minimum Capacity Payments Under PPAs Due, Thereafter	0.0
Total future minimum capacity payments under PPAs due	34.6
Future Minimum Operating Leases Payments Due, 2016	5.7
Future Minimum Operating Leases Payments Due, 2017	5.2
Future Minimum Operating Leases Payments Due, 2018	4.7
Future Minimum Operating Leases Payments Due, 2019	4.4
Future Minimum Operating Leases Payments Due, 2020	4.1
Future Minimum Operating Leases Payments Due, Thereafter	14.5
Total future minimum operating leases payments due	38.6
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2016	218.3
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2017	21.5
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2018	9.6
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2019	9.7
Future Minimum Net Purchase Obligations/Commitments Payments Due, 2020	4.7
Future Minimum Net Purchase Obligations/Commitments Payments Due, Thereafter	20.0
Total future minimum net purchase obligations/commitments payments due	283.8
Future Minimum Payments Due, 2016	238.6
Future Minimum Payments Due, 2017	36.6
Future Minimum Payments Due, 2018	24.4
Future Minimum Payments Due, 2019	14.1
Future Minimum Payments Due, 2020	8.8
Future Minimum Payments Due, Thereafter	34.5
Total future minimum payments	$ 357.0