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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Summary Of Significant Accounting Policies [Line Items]      
Unbilled revenues $ 63.8us-gaap_UnbilledReceivablesCurrent   $ 86.6us-gaap_UnbilledReceivablesCurrent
Franchise fees and gross receipts taxes 27.4te_FranchiseFeesAndGrossReceiptsTaxes 27.2te_FranchiseFeesAndGrossReceiptsTaxes  
Tampa Electric Company [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Unbilled revenues 52.5us-gaap_UnbilledReceivablesCurrent
/ dei_LegalEntityAxis
= us-gaap_AffiliatedEntityMember		   49.3us-gaap_UnbilledReceivablesCurrent
/ dei_LegalEntityAxis
= us-gaap_AffiliatedEntityMember
Franchise fees and gross receipts taxes $ 27.4te_FranchiseFeesAndGrossReceiptsTaxes
/ dei_LegalEntityAxis
= us-gaap_AffiliatedEntityMember		 $ 27.2te_FranchiseFeesAndGrossReceiptsTaxes
/ dei_LegalEntityAxis
= us-gaap_AffiliatedEntityMember