Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	9 Months Ended		0 Months Ended	9 Months Ended
	Feb. 08, 2011 SubrogationLawsuits InsuranceCarrier	Sep. 30, 2014 Claims	Mar. 31, 2011 Customers	Dec. 19, 2013 TECO Guatemala Holdings, LLC v. The Republic of Guatemala [Member]	Sep. 30, 2014 TECO Guatemala Holdings, LLC v. The Republic of Guatemala [Member]	Feb. 08, 2011 Gas Shortages [Member] Customers	Sep. 30, 2014 PGS [Member]	Sep. 30, 2014 PGS [Member] Tampa Electric Company [Member]
Site Contingency [Line Items]
Gas supply disruption of high utility customers			32,000			28,700
Number of class dismissed		2
Period of appeal expires		30 days
Right to appeal expiration date		October 2014
Number of lawsuits for insurance carriers	2
Number of subrogation lawsuits	18
litigation settlement interest					U.S. prime rate plus 2%.
litigation settlement amount				$ 7.5
Settlement agreement payment term					120 days after the date of the Award
Duration of annulment proceedings		2 years
Ultimate financial liability to superfund sites and former MGP sites							$ 33.3	$ 33.3