Short-Term Debt - Credit Facilities (Detail) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Line Of Credit Facility [Line Items]
Credit Facilities	$ 900,000,000	$ 900,000,000
Borrowings Outstanding	128,000,000	139,000,000
Letters of Credit Outstanding	2,200,000	2,300,000
Tampa Electric Company [Member]
Line Of Credit Facility [Line Items]
Credit Facilities	475,000,000	475,000,000
Borrowings Outstanding	0	58,000,000
Letters of Credit Outstanding	500,000	600,000
Tampa Electric Company [Member] | 5-year Facility [Member]
Line Of Credit Facility [Line Items]
Credit Facilities	325,000,000	325,000,000
Borrowings Outstanding	0	12,000,000
Letters of Credit Outstanding	500,000	600,000
Tampa Electric Company [Member] | 3-year Accounts Receivable Facility [Member]
Line Of Credit Facility [Line Items]
Credit Facilities	150,000,000	150,000,000
Borrowings Outstanding	0	46,000,000
Letters of Credit Outstanding	0	0
TECO Energy [Member] | 5-year Facility [Member]
Line Of Credit Facility [Line Items]
Credit Facilities	300,000,000	300,000,000
Borrowings Outstanding	118,000,000	50,000,000
Letters of Credit Outstanding	0	0
New Mexico Gas Company [Member] | 5-year Facility [Member]
Line Of Credit Facility [Line Items]
Credit Facilities	125,000,000	125,000,000
Borrowings Outstanding	10,000,000	31,000,000
Letters of Credit Outstanding	$ 1,700,000	$ 1,700,000