Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Regulatory assets:
Regulatory assets	$ 382.7	$ 402.1
Less: Current portion	39.4	53.6
Long-term regulatory assets	343.3	348.5
Regulatory liabilities:
Regulatory liabilities	763.1	786.0
Less: Current portion	49.9	57.0
Long-term regulatory liabilities	713.2	729.0
Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	356.2	371.7
Less: Current portion	39.3	52.1
Long-term regulatory assets	316.9	319.6
Regulatory liabilities:
Regulatory liabilities	654.0	678.1
Less: Current portion	49.5	54.7
Long-term regulatory liabilities	604.5	623.4
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	71.7	69.2
Regulatory Tax Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	71.7	69.2
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	27.0	45.1
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	27.0	43.6
Postretirement Benefit Asset [Member]
Regulatory assets:
Regulatory assets	188.8	194.0
Postretirement Benefit Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	183.1	187.8
Deferred Bond Refinancing Costs [Member]
Regulatory assets:
Regulatory assets	6.8	7.2
Deferred Bond Refinancing Costs [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	6.8	7.2
Debt Basis Adjustment [Member]
Regulatory assets:
Regulatory assets	19.2	20.9
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	52.5	53.1
Environmental Remediation [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	52.5	53.1
Competitive Rate Adjustment [Member]
Regulatory assets:
Regulatory assets	2.5	2.8
Competitive Rate Adjustment [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	2.5	2.8
Other [Member]
Regulatory assets:
Regulatory assets	14.2	9.8
Other [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	12.6	8.0
Total Other Regulatory Assets [Member]
Regulatory assets:
Regulatory assets	311.0	332.9
Total Other Regulatory Assets [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	284.5	302.5
Regulatory Tax Liability [Member]
Regulatory liabilities:
Regulatory liabilities	6.3	6.9
Regulatory Tax Liability [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	4.6	5.1
Cost-Recovery Clauses [Member]
Regulatory liabilities:
Regulatory liabilities	20.6	25.9
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	20.2	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
Deferred Gain on Property Sales [Member]
Regulatory liabilities:
Regulatory liabilities	0.2	0.8
Deferred Gain on Property Sales [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	0.2	0.8
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	679.1	695.2
Accumulated Reserve - Cost of Removal [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	572.3	591.5
Other [Member]
Regulatory liabilities:
Regulatory liabilities	0.8	1.1
Other [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	0.6	1.1
Total Other Regulatory Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	756.8	779.1
Total Other Regulatory Liabilities [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	$ 649.4	$ 673.0