Schedule II - Valuation and Qualifying Accounts and Reserves (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 2.6	$ 4.5	$ 3.0
Charged to Income	4.8	3.8	10.7
Other Charges	0	0	0
Payments & Deductions	3.2	5.7	9.2
Balance at End of Period	4.2	2.6	4.5
TAMPA ELECTRIC CO [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	1.3	3.2	1.6
Charged to Income	3.4	3.8	10.7
Other Charges	0	0	0
Payments & Deductions	3.2	5.7	9.1
Balance at End of Period	$ 1.5	$ 1.3	$ 3.2