Other Comprehensive Income - Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized losses from cash flow hedges	$ (7.5)	$ (7.8)
Total accumulated other comprehensive loss	(20.1)	(13.2)
Tampa Electric Company [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net unrealized losses from cash flow hedges	(7.6)	(7.8)
Total accumulated other comprehensive loss	(7.6)	(7.8)
Pension Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrecognized pension loss and prior service credit	(19.7)	(20.5)
Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrecognized other benefit loss, prior service cost and transition obligation	$ 7.1	$ 15.1