Accounting for Derivative Instruments and Hedging Activities - Derivative Volumes Expected to Settle (Detail)	Sep. 30, 2016 MMBTU
Physical [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Physical [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Physical [Member] | Natural Gas Contract Expected to be Settled in Year 2016 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Physical [Member] | Natural Gas Contract Expected to be Settled in Year 2016 [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Physical [Member] | Natural Gas Contract Expected to be Settled in Year 2017 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Physical [Member] | Natural Gas Contract Expected to be Settled in Year 2017 [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Physical [Member] | Natural Gas Contract Expected to be Settled in Year 2018 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Physical [Member] | Natural Gas Contract Expected to be Settled in Year 2018 [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0
Financial [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	52,300,000
Financial [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	36,200,000
Financial [Member] | Natural Gas Contract Expected to be Settled in Year 2016 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	14,200,000
Financial [Member] | Natural Gas Contract Expected to be Settled in Year 2016 [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	7,700,000
Financial [Member] | Natural Gas Contract Expected to be Settled in Year 2017 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	32,800,000
Financial [Member] | Natural Gas Contract Expected to be Settled in Year 2017 [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	23,200,000
Financial [Member] | Natural Gas Contract Expected to be Settled in Year 2018 [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	5,300,000
Financial [Member] | Natural Gas Contract Expected to be Settled in Year 2018 [Member] | Tampa Electric Company [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	5,300,000