Accounting For Derivative Instruments And Hedging Activities (Fair Value Of The Overall Contractual Contingent Liability Positions) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
Fair Value Asset/ (Liability)	$ (44.0)
Derivative Exposure Asset/ (Liability)	(44.0)
Posted Collateral	0
Tampa Electric Co [Member]
Fair Value Asset/ (Liability)	(41.2)
Derivative Exposure Asset/ (Liability)	(41.2)
Posted Collateral	$ 0