Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Regulatory assets:
Regulatory assets	$ 366.5	$ 327.4
Less: Current portion	24.3	34.3
Long-term regulatory assets	342.2	293.1
Regulatory liabilities:
Regulatory liabilities	793.0	717.2
Less: Current portion	65.8	85.8
Long-term regulatory liabilities	727.2	631.4
Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	334.6	327.4
Less: Current portion	22.9	34.3
Long-term regulatory assets	311.7	293.1
Regulatory liabilities:
Regulatory liabilities	688.0	717.2
Less: Current portion	64.5	85.8
Long-term regulatory liabilities	623.5	631.4
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	69.1	67.4
Regulatory Tax Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	68.6	67.4
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	9.3	6.1
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	8.0	6.1
Postretirement Benefit Asset [Member]
Regulatory assets:
Regulatory assets	194.1	182.7
Postretirement Benefit Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	187.8	182.7
Deferred Bond Refinancing Costs [Member]
Regulatory assets:
Regulatory assets	9.2	8.0
Deferred Bond Refinancing Costs [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	7.4	8.0
Deferred Bond Refinancing Costs [Member]
Regulatory assets:
Regulatory assets	21.7	0
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	52.3	51.4
Environmental Remediation [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	52.3	51.4
Competitive Rate Adjustment [Member]
Regulatory assets:
Regulatory assets	2.6	4.1
Competitive Rate Adjustment [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	2.6	4.1
Other [Member]
Regulatory assets:
Regulatory assets	8.2	7.7
Other [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	7.9	7.7
Total Other Regulatory Assets [Member]
Regulatory assets:
Regulatory assets	297.4	260.0
Total Other Regulatory Assets [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	266.0	260.0
Regulatory Tax Liability [Member]
Regulatory liabilities:
Regulatory liabilities	6.7	9.8
Regulatory Tax Liability [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	5.3	9.8
Cost-Recovery Clauses [Member]
Regulatory liabilities:
Regulatory liabilities	34.6	54.5
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	33.1	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	1.1	2.0
Deferred Gain on Property Sales [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	1.1	2.0
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	693.6	594.0
Accumulated Reserve - Cost of Removal [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	591.5	594.0
Other [Member]
Regulatory liabilities:
Regulatory liabilities	0.9	0.8
Other [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	0.9	0.8
Total Other Regulatory Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	786.3	707.4
Total Other Regulatory Liabilities [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	$ 682.7	$ 707.4