Short-Term Debt - Credit Facilities (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Line Of Credit Facility [Line Items]
Credit Facilities	$ 1,300,000,000	$ 900,000,000
Borrowings Outstanding	610,500,000	247,000,000
Letters of Credit Outstanding	1,900,000	2,200,000
Tampa Electric Company [Member]
Line Of Credit Facility [Line Items]
Credit Facilities	475,000,000	475,000,000
Borrowings Outstanding	49,000,000	61,000,000
Letters of Credit Outstanding	500,000	500,000
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	0
Letters of Credit Outstanding	500,000	500,000
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	49,000,000	61,000,000
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	150,000,000	163,000,000
Letters of Credit Outstanding	0	0
TECO Energy [Member] | 1-year Term Facility [Member]
Line Of Credit Facility [Line Items]
Credit Facilities	400,000,000	0
Borrowings Outstanding	400,000,000	0
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	11,500,000	23,000,000
Letters of Credit Outstanding	$ 1,400,000	$ 1,700,000