Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Regulatory assets:
Regulatory assets	$ 317.6	$ 327.4
Less: Current portion	33.7	34.3
Long-term regulatory assets	283.9	293.1
Regulatory liabilities:
Regulatory liabilities	687.1	717.2
Less: Current portion	65.7	85.8
Long-term regulatory liabilities	621.4	631.4
Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	317.6	327.4
Less: Current portion	33.7	34.3
Long-term regulatory assets	283.9	293.1
Regulatory liabilities:
Regulatory liabilities	687.1	717.2
Less: Current portion	65.7	85.8
Long-term regulatory liabilities	621.4	631.4
Regulatory Tax Liability [Member]
Regulatory liabilities:
Regulatory liabilities	5.6	9.8
Regulatory Tax Liability [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	5.6	9.8
Cost-Recovery Clauses [Member]
Regulatory liabilities:
Regulatory liabilities	34.8	54.5
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	34.8	54.5
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	1.4	2.0
Deferred Gain on Property Sales [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	1.4	2.0
Provision for Stipulation and Other [Member]
Regulatory liabilities:
Regulatory liabilities	0.8	0.8
Provision for Stipulation and Other [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	0.8	0.8
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	588.4	594.0
Accumulated Reserve - Cost of Removal [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	588.4	594.0
Total Other Regulatory Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	681.5	707.4
Total Other Regulatory Liabilities [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	681.5	707.4
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	68.1	67.4
Regulatory Tax Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	68.1	67.4
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	1.8	6.1
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	1.8	6.1
Postretirement Benefit Asset [Member]
Regulatory assets:
Regulatory assets	177.6	182.7
Postretirement Benefit Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	177.6	182.7
Deferred Bond Refinancing Costs [Member]
Regulatory assets:
Regulatory assets	7.6	8.0
Deferred Bond Refinancing Costs [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	7.6	8.0
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	52.0	51.4
Environmental Remediation [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	52.0	51.4
Competitive Rate Adjustment [Member]
Regulatory assets:
Regulatory assets	2.8	4.1
Competitive Rate Adjustment [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	2.8	4.1
Other [Member]
Regulatory assets:
Regulatory assets	7.7	7.7
Other [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	7.7	7.7
Total Other Regulatory Assets [Member]
Regulatory assets:
Regulatory assets	249.5	260.0
Total Other Regulatory Assets [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	$ 249.5	$ 260.0