Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Regulatory Assets [Line Items]
Regulatory assets	$ 452.9	$ 451.8
Less: Current portion	70.3	87.3
Long-term regulatory assets	382.6	364.5
Regulatory liabilities	758.6	705.6
Less: Current portion	106.7	86.2
Long-term regulatory liabilities	651.9	619.4
Regulatory tax asset [Member]
Regulatory Assets [Line Items]
Regulatory assets	67.2	63.6
Cost-recovery clauses [Member]
Regulatory Assets [Line Items]
Regulatory assets	42.9	73.3
Regulatory liabilities	73.9	61.4
Postretirement benefit asset [Member]
Regulatory Assets [Line Items]
Regulatory assets	276.1	252.4
Deferred bond refinancing costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	9.2	11.1
Environmental remediation [Member]
Regulatory Assets [Line Items]
Regulatory assets	46.9	30.5
Competitive rate adjustment [Member]
Regulatory Assets [Line Items]
Regulatory assets	4.1	3.5
Total other regulatory assets [Member]
Regulatory Assets [Line Items]
Regulatory assets	6.5	17.4
Total other regulatory assets [Member]
Regulatory Assets [Line Items]
Regulatory assets	385.7	388.2
Deferred income tax charges [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	14.6	16.0
Transmission and delivery storm reserve [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	50.4	43.6
Deferred gain on property sales [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	3.4	5.0
Provision for stipulation and other [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	1.0	0.8
Accumulated reserve - cost of removal [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	615.3	578.8
Total other regulatory liabilities [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	744.0	689.6
TAMPA ELECTRIC CO [Member]
Regulatory Assets [Line Items]
Regulatory assets	452.9	451.8
Less: Current portion	70.3	87.3
Long-term regulatory assets	382.6	364.5
Regulatory liabilities	758.6	705.6
Less: Current portion	106.7	86.2
Long-term regulatory liabilities	651.9	619.4
TAMPA ELECTRIC CO [Member] | Regulatory tax asset [Member]
Regulatory Assets [Line Items]
Regulatory assets	67.2	63.6
TAMPA ELECTRIC CO [Member] | Cost-recovery clauses [Member]
Regulatory Assets [Line Items]
Regulatory assets	42.9	73.3
Regulatory liabilities	73.9	61.4
TAMPA ELECTRIC CO [Member] | Postretirement benefit asset [Member]
Regulatory Assets [Line Items]
Regulatory assets	276.1	252.4
TAMPA ELECTRIC CO [Member] | Deferred bond refinancing costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	9.2	11.1
TAMPA ELECTRIC CO [Member] | Environmental remediation [Member]
Regulatory Assets [Line Items]
Regulatory assets	46.9	30.5
TAMPA ELECTRIC CO [Member] | Competitive rate adjustment [Member]
Regulatory Assets [Line Items]
Regulatory assets	4.1	3.5
TAMPA ELECTRIC CO [Member] | Total other regulatory assets [Member]
Regulatory Assets [Line Items]
Regulatory assets	6.5	17.4
TAMPA ELECTRIC CO [Member] | Total other regulatory assets [Member]
Regulatory Assets [Line Items]
Regulatory assets	385.7	388.2
TAMPA ELECTRIC CO [Member] | Deferred income tax charges [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	14.6	16.0
TAMPA ELECTRIC CO [Member] | Transmission and delivery storm reserve [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	50.4	43.6
TAMPA ELECTRIC CO [Member] | Deferred gain on property sales [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	3.4	5.0
TAMPA ELECTRIC CO [Member] | Provision for stipulation and other [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	1.0	0.8
TAMPA ELECTRIC CO [Member] | Accumulated reserve - cost of removal [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	615.3	578.8
TAMPA ELECTRIC CO [Member] | Total other regulatory liabilities [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	$ 744.0	$ 689.6