Consolidated Statements of Capitalization - Long-Term Debt (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt, total	$ 2,182.6	$ 2,265.9
Unamortized debt discount, net	(3.0)	(2.8)
Debt issuance costs	(16.7)	(18.1)
Long-term debt, carrying amount	2,162.9	2,245.0
Less amount due within one year	0.0	83.3
Total long-term debt	2,162.9	2,161.7
Long-term debt, fair value	2,345.3	2,433.3
Level 1 [Member]
Debt Instrument [Line Items]
Long-term debt, fair value	57.9
Tampa Electric [Member]
Debt Instrument [Line Items]
Long-term debt, total	1,920.9	2,004.2
Long-term debt, carrying amount	$ 1,920.9
Tampa Electric [Member] \| 5.65% Refunding bonds [Member]
Debt Instrument [Line Items]
Due	2018
Long-term debt, total	$ 54.2	54.2
Tampa Electric [Member] \| 6.25% Notes [Member]
Debt Instrument [Line Items]
Due	2016
Long-term debt, total	$ 0.0	83.3
Tampa Electric [Member] \| 6.10% Notes [Member]
Debt Instrument [Line Items]
Due	2018
Long-term debt, total	$ 200.0	200.0
Tampa Electric [Member] \| 5.40% Notes [Member]
Debt Instrument [Line Items]
Due	2021
Long-term debt, total	$ 231.7	231.7
Tampa Electric [Member] \| 2.60% Notes [Member]
Debt Instrument [Line Items]
Due	2022
Long-term debt, total	$ 225.0	225.0
Tampa Electric [Member] \| 6.55% Notes [Member]
Debt Instrument [Line Items]
Due	2036
Long-term debt, total	$ 250.0	250.0
Tampa Electric [Member] \| 6.15% Notes [Member]
Debt Instrument [Line Items]
Due	2037
Long-term debt, total	$ 190.0	190.0
Tampa Electric [Member] \| 4.10% Notes [Member]
Debt Instrument [Line Items]
Due	2042
Long-term debt, total	$ 250.0	250.0
Tampa Electric [Member] \| 4.35% Notes [Member]
Debt Instrument [Line Items]
Due	2044
Long-term debt, total	$ 290.0	290.0
Tampa Electric [Member] \| 4.20% Notes [Member]
Debt Instrument [Line Items]
Due	2045
Long-term debt, total	$ 230.0	230.0
PGS [Member]
Debt Instrument [Line Items]
Long-term debt, total	261.7	261.7
Long-term debt, carrying amount	$ 261.7
PGS [Member] \| 6.10% Notes [Member]
Debt Instrument [Line Items]
Due	2018
Long-term debt, total	$ 50.0	50.0
PGS [Member] \| 5.40% Notes [Member]
Debt Instrument [Line Items]
Due	2021
Long-term debt, total	$ 46.7	46.7
PGS [Member] \| 2.60% Notes [Member]
Debt Instrument [Line Items]
Due	2022
Long-term debt, total	$ 25.0	25.0
PGS [Member] \| 6.15% Notes [Member]
Debt Instrument [Line Items]
Due	2037
Long-term debt, total	$ 60.0	60.0
PGS [Member] \| 4.10% Notes [Member]
Debt Instrument [Line Items]
Due	2042
Long-term debt, total	$ 50.0	50.0
PGS [Member] \| 4.35% Notes [Member]
Debt Instrument [Line Items]
Due	2044
Long-term debt, total	$ 10.0	10.0
PGS [Member] \| 4.20% Notes [Member]
Debt Instrument [Line Items]
Due	2045
Long-term debt, total	$ 20.0	$ 20.0

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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