Other Comprehensive Income - Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross	$ 1.1	$ 2.5	$ 0.7	$ (7.2)
Reclassification from AOCI to net income, Gross	0.1	0.2	1.0	0.5
Gain (Loss) Gain on cash flow hedges, Gross	1.2	2.7	1.7	(6.7)
Amortization of unrecognized benefit costs, Gross	1.0	0.8	3.2	2.3
Recognized benefit costs due to settlement, Gross	2.6		2.6
Total other comprehensive income (loss) , Gross	4.8	3.5	7.5	(4.4)
Unrealized gain (loss) on cash flow hedges, Tax	(0.4)	(0.9)	(0.3)	2.7
Reclassification from AOCI to net income, Tax	0	(0.1)	(0.3)	(0.2)
Gain (Loss) on cash flow hedges, Tax	(0.4)	(1.0)	(0.6)	2.5
Amortization of unrecognized benefit costs, Tax	(0.4)	(0.3)	(1.2)	(1.2)
Recognized benefit costs due to settlement, Tax	(1.0)		(1.0)
Total other comprehensive income (loss) , Tax	(1.8)	(1.3)	(2.8)	1.3
Unrealized gain (loss) on cash flow hedges, Net	0.7	1.6	0.4	(4.5)
Reclassification from AOCI to net income, Net	0.1	0.1	0.7	0.3
Gain (Loss) on cash flow hedges, Net	0.8	1.7	1.1	(4.2)
Amortization of unrecognized benefit costs, Net	0.6	0.5	2.0	1.1
Recognized benefit costs due to settlement, Net	1.6		1.6
Other comprehensive income (loss), net of tax	3.0	2.2	4.7	(3.1)
Tampa Electric Company [Member]
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross	0	0	0	(8.0)
Reclassification from AOCI to net income, Gross	0.4	0.4	1.1	1.0
Gain (Loss) Gain on cash flow hedges, Gross	0.4	0.4	1.1	(7.0)
Total other comprehensive income (loss) , Gross	0.4	0.4	1.1	(7.0)
Unrealized gain (loss) on cash flow hedges, Tax	0	0	0	3.1
Reclassification from AOCI to net income, Tax	(0.2)	(0.2)	(0.4)	(0.4)
Gain (Loss) on cash flow hedges, Tax	(0.2)	(0.2)	(0.4)	2.7
Total other comprehensive income (loss) , Tax	(0.2)	(0.2)	(0.4)	2.7
Unrealized gain (loss) on cash flow hedges, Net	0	0	0	(4.9)
Reclassification from AOCI to net income, Net	0.2	0.2	0.7	0.6
Gain (Loss) on cash flow hedges, Net	0.2	0.2	0.7	(4.3)
Other comprehensive income (loss), net of tax	$ 0.2	$ 0.2	$ 0.7	$ (4.3)