Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Regulatory assets:
Regulatory assets	$ 440.0	$ 402.1
Less: Current portion	44.8	53.6
Long-term regulatory assets	395.2	348.5
Regulatory liabilities:
Regulatory liabilities	800.6	786.0
Less: Current portion	84.8	57.0
Long-term regulatory liabilities	715.8	729.0
Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	418.1	371.7
Less: Current portion	44.3	52.1
Long-term regulatory assets	373.8	319.6
Regulatory liabilities:
Regulatory liabilities	686.7	678.1
Less: Current portion	83.2	54.7
Long-term regulatory liabilities	603.5	623.4
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	74.7	69.2
Regulatory Tax Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	74.6	69.2
Cost-Recovery Clauses - Deferred Balances [Member]
Regulatory assets:
Regulatory assets	5.5	1.9
Cost-Recovery Clauses - Deferred Balances [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	5.2	0.9
Cost-Recovery Clauses - Offsets to Derivative Liabilities [Member]
Regulatory assets:
Regulatory assets	26.5	43.2
Cost-Recovery Clauses - Offsets to Derivative Liabilities [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	26.2	42.7
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	54.0	53.1
Environmental Remediation [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	54.0	53.1
Postretirement Benefit Costs [Member]
Regulatory assets:
Regulatory assets	240.6	194.0
Postretirement Benefit Costs [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	238.3	187.8
Deferred Bond Refinancing Costs [Member]
Regulatory assets:
Regulatory assets	6.5	7.2
Deferred Bond Refinancing Costs [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	6.5	7.2
Debt Basis Adjustment [Member]
Regulatory assets:
Regulatory assets	17.5	20.9
Competitive Rate Adjustment [Member]
Regulatory assets:
Regulatory assets	2.6	2.8
Competitive Rate Adjustment [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	2.6	2.8
Other [Member]
Regulatory assets:
Regulatory assets	12.1	9.8
Other [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	10.7	8.0
Regulatory Tax Liability [Member]
Regulatory liabilities:
Regulatory liabilities	7.9	6.9
Regulatory Tax Liability [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	5.7	5.1
Cost-Recovery Clauses [Member]
Regulatory liabilities:
Regulatory liabilities	55.9	25.9
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	54.2	23.5
Transmission and Delivery Storm Reserve [Member]
Regulatory liabilities:
Regulatory liabilities	56.1	56.1
Transmission and Delivery Storm Reserve [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	56.1	56.1
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	679.9	695.2
Accumulated Reserve - Cost of Removal [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	570.0	591.5
Other [Member]
Regulatory liabilities:
Regulatory liabilities	0.8	1.9
Other [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	$ 0.7	$ 1.9