Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Regulatory assets:
Regulatory assets	$ 411.4	$ 452.9
Less: Current portion	40.9	70.3
Long-term regulatory assets	370.5	382.6
Regulatory liabilities
Regulatory liabilities	714.0	737.0
Regulatory liabilities	714.0	737.0
Less: Current portion	81.3	105.6
Long-term regulatory liabilities	632.7	631.4
Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	411.4	452.9
Less: Current portion	40.9	70.3
Long-term regulatory assets	370.5	382.6
Regulatory liabilities
Regulatory liabilities	714.0	737.0
Regulatory liabilities	714.0	737.0
Less: Current portion	81.3	105.6
Long-term regulatory liabilities	632.7	631.4
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	67.2	67.2
Regulatory Tax Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	67.2	67.2
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	14.4	42.9
Regulatory liabilities
Regulatory liabilities	49.4	73.9
Regulatory liabilities	49.4	73.9
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	14.4	42.9
Regulatory liabilities
Regulatory liabilities	49.4	73.9
Regulatory liabilities	49.4	73.9
Postretirement Benefit Asset [Member]
Regulatory assets:
Regulatory assets	263.8	276.1
Postretirement Benefit Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	263.8	276.1
Deferred Bond Refinancing Costs [Member]
Regulatory assets:
Regulatory assets	8.3	9.2
Deferred Bond Refinancing Costs [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	8.3	9.2
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	47.8	46.9
Environmental Remediation [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	47.8	46.9
Competitive Rate Adjustment [Member]
Regulatory assets:
Regulatory assets	4.2	4.1
Competitive Rate Adjustment [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	4.2	4.1
Other [Member]
Regulatory assets:
Regulatory assets	5.7	6.5
Other [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	5.7	6.5
Total Other Regulatory Assets [Member]
Regulatory assets:
Regulatory assets	344.2	385.7
Total Other Regulatory Assets [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	344.2	385.7
Regulatory Tax Liability [Member]
Regulatory liabilities
Regulatory liabilities	13.7	14.6
Regulatory liabilities	13.7	14.6
Regulatory Tax Liability [Member] | Tampa Electric Company [Member]
Regulatory liabilities
Regulatory liabilities	13.7	14.6
Regulatory liabilities	13.7	14.6
Transmission and Delivery Storm Reserve [Member]
Regulatory liabilities
Regulatory liabilities	55.4	50.4
Regulatory liabilities	55.4	50.4
Transmission and Delivery Storm Reserve [Member] | Tampa Electric Company [Member]
Regulatory liabilities
Regulatory liabilities	55.4	50.4
Regulatory liabilities	55.4	50.4
Deferred Gain on Property Sales [Member]
Regulatory liabilities
Regulatory liabilities	2.3	3.4
Regulatory liabilities	2.3	3.4
Deferred Gain on Property Sales [Member] | Tampa Electric Company [Member]
Regulatory liabilities
Regulatory liabilities	2.3	3.4
Regulatory liabilities	2.3	3.4
Other [Member]
Regulatory liabilities
Regulatory liabilities	1.3	1.0
Regulatory liabilities	1.3	1.0
Other [Member] | Tampa Electric Company [Member]
Regulatory liabilities
Regulatory liabilities	1.3	1.0
Regulatory liabilities	1.3	1.0
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities
Regulatory liabilities	591.9	593.7
Regulatory liabilities	591.9	593.7
Accumulated Reserve - Cost of Removal [Member] | Tampa Electric Company [Member]
Regulatory liabilities
Regulatory liabilities	591.9	593.7
Regulatory liabilities	591.9	593.7
Total Other Regulatory Liabilities [Member]
Regulatory liabilities
Regulatory liabilities	700.3	722.4
Regulatory liabilities	700.3	722.4
Total Other Regulatory Liabilities [Member] | Tampa Electric Company [Member]
Regulatory liabilities
Regulatory liabilities	700.3	722.4
Regulatory liabilities	$ 700.3	$ 722.4