Long-Term Debt - Schedule of Long Term Debt Outstanding (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Long-term debt, total	$ 3,835.9	$ 3,610.5
Unamortized debt discount, net	14.3	18.0
Total long-term debt maturities	3,850.2	3,628.5
Less amount due within one year	333.3	274.5
Total long-term debt	3,516.9	3,354.0
PGS [Member]
Debt Instrument [Line Items]
Long-term debt, total	261.7	241.7
TECO Finance [Member]
Debt Instrument [Line Items]
Long-term debt, total	1,100.0	1,041.2
Tampa Electric Company [Member]
Debt Instrument [Line Items]
Long-term debt, total	2,265.9	2,099.3
Unamortized debt discount, net	(2.8)	(2.2)
Total long-term debt maturities	2,263.1	2,097.1
Less amount due within one year	83.3	83.3
Total long-term debt	2,179.8	2,013.8
Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Long-term debt, total	2,004.2	1,857.6
Total long-term debt maturities	2,004.2
Tampa Electric Company [Member] | PGS [Member]
Debt Instrument [Line Items]
Long-term debt, total	261.7	241.7
Total long-term debt maturities	261.7
NMGI [Member]
Debt Instrument [Line Items]
Long-term debt, total	200.0	200.0
NMGC [Member]
Debt Instrument [Line Items]
Long-term debt, total	$ 270.0	270.0
6.75% Notes [Member] | TECO Finance [Member]
Debt Instrument [Line Items]
Due	2015
Long-term debt, total	$ 0.0	191.2
4.00% Notes [Member] | TECO Finance [Member]
Debt Instrument [Line Items]
Due	2016
Long-term debt, total	$ 250.0	250.0
6.57% Notes [Member] | TECO Finance [Member]
Debt Instrument [Line Items]
Due	2017
Long-term debt, total	$ 300.0	300.0
Floating Rate Notes [Member] | TECO Finance [Member]
Debt Instrument [Line Items]
Due	2018
Long-term debt, total	$ 250.0	0.0
5.15% Notes [Member] | TECO Finance [Member]
Debt Instrument [Line Items]
Due	2020
Long-term debt, total	$ 300.0	300.0
5.65% Refunding bonds [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2018
Long-term debt, total	$ 54.2	54.2
Variable Rate Bonds Repurchased In 2008 [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2020
Long-term debt, total	$ 0.0	0.0
5.15% Refunding bonds [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2025
Long-term debt, total	$ 0.0	0.0
1.5% term rate bonds repurchased in 2011 [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2030
Long-term debt, total	$ 0.0	0.0
5.0% Refunding bonds [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2034
Long-term debt, total	$ 0.0	0.0
6.25% Notes [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Maturity range start	2015
Maturity range end	2016
Long-term debt, total	$ 83.3	166.7
6.10% Notes [Member] | PGS [Member]
Debt Instrument [Line Items]
Due	2018
Long-term debt, total	$ 50.0	50.0
6.10% Notes [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2018
Long-term debt, total	$ 200.0	200.0
5.40% Notes [Member] | PGS [Member]
Debt Instrument [Line Items]
Due	2021
Long-term debt, total	$ 46.7	46.7
5.40% Notes [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2021
Long-term debt, total	$ 231.7	231.7
2.60% Notes [Member] | PGS [Member]
Debt Instrument [Line Items]
Due	2022
Long-term debt, total	$ 25.0	25.0
2.60% Notes [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2022
Long-term debt, total	$ 225.0	225.0
6.55% Notes [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2036
Long-term debt, total	$ 250.0	250.0
6.15% Notes [Member] | PGS [Member]
Debt Instrument [Line Items]
Due	2037
Long-term debt, total	$ 60.0	60.0
6.15% Notes [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2037
Long-term debt, total	$ 190.0	190.0
4.10% Notes [Member] | PGS [Member]
Debt Instrument [Line Items]
Due	2042
Long-term debt, total	$ 50.0	50.0
4.10% Notes [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2042
Long-term debt, total	$ 250.0	250.0
4.35% Notes [Member] | PGS [Member]
Debt Instrument [Line Items]
Due	2044
Long-term debt, total	$ 10.0	10.0
4.35% Notes [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2044
Long-term debt, total	$ 290.0	290.0
4.20% Notes [Member] | PGS [Member]
Debt Instrument [Line Items]
Due	2045
Long-term debt, total	$ 20.0	0.0
4.20% Notes [Member] | Tampa Electric Company [Member] | Tampa Electric [Member]
Debt Instrument [Line Items]
Due	2045
Long-term debt, total	$ 230.0	0.0
2.71 % Notes [Member] | NMGI [Member]
Debt Instrument [Line Items]
Due	2019
Long-term debt, total	$ 50.0	50.0
3.64 % Notes [Member] | NMGI [Member]
Debt Instrument [Line Items]
Due	2024
Long-term debt, total	$ 150.0	150.0
4.87 % Notes [Member] | NMGC [Member]
Debt Instrument [Line Items]
Due	2021
Long-term debt, total	$ 200.0	200.0
3.54 % Notes [Member] | NMGC [Member]
Debt Instrument [Line Items]
Due	2026
Long-term debt, total	$ 70.0	$ 70.0