Consolidated Statements of Capitalization - Long-Term Debt (Parenthetical) (Detail) - Tampa Electric Company [Member] - USD ($) $ in Millions	Dec. 31, 2015	Sep. 30, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2008
Tampa Electric [Member] | 5.65% Refunding bonds [Member]
Debt Instrument [Line Items]
Stated interest rate	5.65%
Tampa Electric [Member] | 5.15% Refunding bonds [Member]
Debt Instrument [Line Items]
Stated interest rate	5.15%
Variable rate bonds, par amounts		$ 51.6
Tampa Electric [Member] | 1.5% term rate bonds repurchased in 2011 [Member]
Debt Instrument [Line Items]
Stated interest rate	1.50%
Variable rate bonds, par amounts				$ 75.0
Tampa Electric [Member] | 5.0% Refunding bonds [Member]
Debt Instrument [Line Items]
Stated interest rate	5.00%
Tampa Electric [Member] | 6.25% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	6.25%
Tampa Electric [Member] | 6.10% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	6.10%
Tampa Electric [Member] | 5.40% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	5.40%
Tampa Electric [Member] | 2.60% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	2.60%
Tampa Electric [Member] | 6.55% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	6.55%
Tampa Electric [Member] | 6.15% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	6.15%
Tampa Electric [Member] | 4.10% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	4.10%
Tampa Electric [Member] | 4.35% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	4.35%
Tampa Electric [Member] | 4.20% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	4.20%
Tampa Electric [Member] | Variable rate bonds repurchased in 2008 Due To 2020 [Member]
Debt Instrument [Line Items]
Variable rate bonds, par amounts					$ 20.0
Tampa Electric [Member] | Variable Rate Bonds
Debt Instrument [Line Items]
Variable rate bonds, par amounts			$ 86.0
PGS [Member] | 6.10% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	6.10%
PGS [Member] | 5.40% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	5.40%
PGS [Member] | 2.60% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	2.60%
PGS [Member] | 6.15% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	6.15%
PGS [Member] | 4.10% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	4.10%
PGS [Member] | 4.35% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	4.35%
PGS [Member] | 4.20% Notes [Member]
Debt Instrument [Line Items]
Stated interest rate	4.20%