Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Regulatory assets:
Regulatory assets	$ 402.0	$ 402.1
Less: Current portion	52.0	53.6
Long-term regulatory assets	350.0	348.5
Regulatory liabilities:
Regulatory liabilities	769.4	786.0
Less: Current portion	49.4	57.0
Long-term regulatory liabilities	720.0	729.0
Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	373.9	371.7
Less: Current portion	51.6	52.1
Long-term regulatory assets	322.3	319.6
Regulatory liabilities:
Regulatory liabilities	661.7	678.1
Less: Current portion	48.8	54.7
Long-term regulatory liabilities	612.9	623.4
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	70.5	69.2
Regulatory Tax Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	70.5	69.2
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	42.8	45.1
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	42.4	43.6
Postretirement Benefit Asset [Member]
Regulatory assets:
Regulatory assets	195.6	194.0
Postretirement Benefit Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	189.7	187.8
Deferred Bond Refinancing Costs [Member]
Regulatory assets:
Regulatory assets	7.0	7.2
Deferred Bond Refinancing Costs [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	7.0	7.2
Debt Basis Adjustment [Member]
Regulatory assets:
Regulatory assets	20.1	20.9
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	53.4	53.1
Environmental Remediation [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	53.4	53.1
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	10.0	9.8
Other [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	8.3	8.0
Total Other Regulatory Assets [Member]
Regulatory assets:
Regulatory assets	331.5	332.9
Total Other Regulatory Assets [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	303.4	302.5
Regulatory Tax Liability [Member]
Regulatory liabilities:
Regulatory liabilities	6.6	6.9
Regulatory Tax Liability [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	4.9	5.1
Cost-Recovery Clauses [Member]
Regulatory liabilities:
Regulatory liabilities	19.4	25.9
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	18.8	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	0.5	0.8
Deferred Gain on Property Sales [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	0.5	0.8
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	686.0	695.2
Accumulated Reserve - Cost of Removal [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	580.7	591.5
Other [Member]
Regulatory liabilities:
Regulatory liabilities	0.8	1.1
Other [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	0.7	1.1
Total Other Regulatory Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	762.8	779.1
Total Other Regulatory Liabilities [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	$ 656.8	$ 673.0