Short-Term Debt - Credit Facilities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Dec. 17, 2013	Sep. 30, 2014 Tampa Electric Company [Member]	Dec. 31, 2013 Tampa Electric Company [Member]	Sep. 30, 2014 Tampa Electric Company [Member] 5-year Facility [Member]	Dec. 31, 2013 Tampa Electric Company [Member] 5-year Facility [Member]	Sep. 30, 2014 Tampa Electric Company [Member] 1-year Accounts Receivable Facility [Member]	Feb. 14, 2014 Tampa Electric Company [Member] 1-year Accounts Receivable Facility [Member]	Dec. 31, 2013 Tampa Electric Company [Member] 1-year Accounts Receivable Facility [Member]	Sep. 30, 2014 TECO Energy [Member] 5-year Facility [Member]	Dec. 31, 2013 TECO Energy [Member] 5-year Facility [Member]	Sep. 30, 2014 New Mexico Gas Company [Member] 5-year Facility [Member]	Dec. 31, 2013 New Mexico Gas Company [Member] 5-year Facility [Member]
Line Of Credit Facility [Line Items]
Credit Facilities	$ 900.0	$ 675.0	$ 40.0	$ 475.0	$ 475.0	$ 325.0	$ 325.0	$ 150.0	$ 150.0	$ 150.0	$ 300.0	$ 200.0	$ 125.0	$ 0
Borrowings Outstanding	72.0	84.0		0	84.0	0	6.0	0		78.0	55.0	0	17.0	0
Letters of Credit Outstanding	$ 2.4	$ 0.7		$ 0.7	$ 0.7	$ 0.7	$ 0.7	$ 0		$ 0	$ 0	$ 0	$ 1.7	$ 0