Accounting for Derivative Instruments and Hedging Activities - Derivative Volumes Expected to Settle (Detail)	Dec. 31, 2012 gal
Diesel Fuel Derivatives [Member] | Physical [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Diesel Fuel Derivatives [Member] | Physical [Member] | 2013 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Diesel Fuel Derivatives [Member] | Physical [Member] | 2014 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Diesel Fuel Derivatives [Member] | Financial [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	4,500,000
Diesel Fuel Derivatives [Member] | Financial [Member] | 2013 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	3,000,000
Diesel Fuel Derivatives [Member] | Financial [Member] | 2014 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1,500,000
Natural Gas Contracts [Member] | Physical [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Natural Gas Contracts [Member] | Physical [Member] | TAMPA ELECTRIC CO [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Natural Gas Contracts [Member] | Physical [Member] | 2013 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Natural Gas Contracts [Member] | Physical [Member] | 2013 [Member] | TAMPA ELECTRIC CO [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Natural Gas Contracts [Member] | Physical [Member] | 2014 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Natural Gas Contracts [Member] | Physical [Member] | 2014 [Member] | TAMPA ELECTRIC CO [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Natural Gas Contracts [Member] | Financial [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	40,600,000
Natural Gas Contracts [Member] | Financial [Member] | TAMPA ELECTRIC CO [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	40,600,000
Natural Gas Contracts [Member] | Financial [Member] | 2013 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	34,200,000
Natural Gas Contracts [Member] | Financial [Member] | 2013 [Member] | TAMPA ELECTRIC CO [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	34,200,000
Natural Gas Contracts [Member] | Financial [Member] | 2014 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	6,400,000
Natural Gas Contracts [Member] | Financial [Member] | 2014 [Member] | TAMPA ELECTRIC CO [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	6,400,000