Commitments and Contingencies - Additional Information (Detail) $ in Millions			9 Months Ended
	Dec. 19, 2013 USD ($)	Feb. 08, 2011 Customer Lawsuit InsuranceCarrier	Sep. 30, 2015 USD ($) Claims	Mar. 31, 2011 Customer
Long Term Commitments [Line Items]
Gas supply disruption of high utility customers | Customer				32,000
Number of claims dismissed | Claims			2
Number of lawsuits for insurance carriers | Lawsuit		2
Number of insurance carriers | InsuranceCarrier		18
PGS [Member]
Long Term Commitments [Line Items]
Ultimate financial liability to superfund sites and former MGP sites			$ 33.3
PGS [Member] | Tampa Electric Company [Member]
Long Term Commitments [Line Items]
Ultimate financial liability to superfund sites and former MGP sites			$ 33.3
TECO Guatemala Holdings, LLC v. The Republic of Guatemala [Member]
Long Term Commitments [Line Items]
Litigation settlement amount	$ 7.5
Damages awarded	$ 21.1
TECO Guatemala Holdings, LLC v. The Republic of Guatemala [Member] | U.S. prime rate plus [Member]
Long Term Commitments [Line Items]
Litigation settlement interest	2.00%
Gas Shortages [Member]
Long Term Commitments [Line Items]
Gas supply disruption of high utility customers | Customer		28,700