Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Regulatory assets:
Regulatory assets	$ 433.6	$ 440.0
Less: Current portion	40.2	44.8
Long-term regulatory assets	393.4	395.2
Regulatory liabilities:
Regulatory liabilities	817.8	800.6
Less: Current portion	108.4	84.8
Long-term regulatory liabilities	709.4	715.8
Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	413.0	418.1
Less: Current portion	39.9	44.3
Long-term regulatory assets	373.1	373.8
Regulatory liabilities:
Regulatory liabilities	700.0	686.7
Less: Current portion	104.5	83.2
Long-term regulatory liabilities	595.5	603.5
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	77.1	74.7
Regulatory Tax Asset [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	77.0	74.6
Cost-Recovery Clauses - Deferred Balances [Member]
Regulatory assets:
Regulatory assets	0.1	5.5
Cost-Recovery Clauses - Deferred Balances [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	0.0	5.2
Cost-Recovery Clauses - Offsets to Derivative Liabilities [Member]
Regulatory assets:
Regulatory assets	26.0	26.5
Cost-Recovery Clauses - Offsets to Derivative Liabilities [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	25.9	26.2
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	54.4	54.0
Environmental Remediation [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	54.4	54.0
Postretirement Benefit Costs [Member]
Regulatory assets:
Regulatory assets	238.5	240.6
Postretirement Benefit Costs [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	236.4	238.3
Deferred Bond Refinancing Costs [Member]
Regulatory assets:
Regulatory assets	6.2	6.5
Deferred Bond Refinancing Costs [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	6.2	6.5
Debt Basis Adjustment [Member]
Regulatory assets:
Regulatory assets	16.7	17.5
Competitive Rate Adjustment [Member]
Regulatory assets:
Regulatory assets	2.5	2.6
Competitive Rate Adjustment [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	2.5	2.6
Other [Member]
Regulatory assets:
Regulatory assets	12.1	12.1
Other [Member] | Tampa Electric Company [Member]
Regulatory assets:
Regulatory assets	10.6	10.7
Regulatory Tax Liability [Member]
Regulatory liabilities:
Regulatory liabilities	7.6	7.9
Regulatory Tax Liability [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	5.6	5.7
Cost-Recovery Clauses [Member]
Regulatory liabilities:
Regulatory liabilities	80.0	55.9
Cost-Recovery Clauses [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	76.1	54.2
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
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	673.6	679.9
Accumulated Reserve - Cost of Removal [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	561.7	570.0
Other [Member]
Regulatory liabilities:
Regulatory liabilities	0.5	0.8
Other [Member] | Tampa Electric Company [Member]
Regulatory liabilities:
Regulatory liabilities	$ 0.5	$ 0.7