Other Comprehensive Income - Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross	$ 1.0	$ (7.4)	$ 1.8
Reclassification from AOCI to net income, Gross	1.3	0.6	(3.1)
Gain (Loss) Gain on cash flow hedges, Gross	2.3	(6.8)	(1.3)
Amortization of unrecognized benefit costs and other, Gross	23.6	(4.8)	(7.9)
Recognized benefit costs due to settlement, Gross	2.6		0.9
Total other comprehensive (loss) income, Gross	28.5	(11.6)	(8.3)
Unrealized gain (loss) on cash flow hedges, Tax	(0.4)	2.8	(0.6)
Reclassification from AOCI to net income, Tax	(0.5)	(0.2)	1.1
Gain (Loss) on cash flow hedges, Tax	(0.9)	2.6	0.5
Amortization of unrecognized benefit costs and other, Tax	(8.8)	0	3.3
Recognized benefit costs due to settlement, Tax	(1.0)		(0.3)
Total other comprehensive (loss) income, Tax	(10.7)	2.6	3.5
Unrealized gain (loss) on cash flow hedges, Net	0.6	(4.6)	1.2
Reclassification from AOCI to net income, Net	0.8	0.4	(2.0)
Gain (Loss) on cash flow hedges, Net	1.4	(4.2)	(0.8)
Amortization of unrecognized benefit costs and other, Net	14.8	(4.8)	(4.6)
Recognized benefit costs due to settlement, Net	1.6		0.6
Other comprehensive income (loss), net of tax	17.8	(9.0)	(4.8)
Tampa Electric Company [Member]
Other Comprehensive Income Loss [Line Items]
Unrealized gain (loss) on cash flow hedges, Gross	0	(8.0)	0
Reclassification from AOCI to net income, Gross	1.4	1.4	1.2
Gain (Loss) Gain on cash flow hedges, Gross	1.4	(6.6)	1.2
Total other comprehensive (loss) income, Gross	1.4	(6.6)	1.2
Unrealized gain (loss) on cash flow hedges, Tax	0	3.1	0
Reclassification from AOCI to net income, Tax	(0.5)	(0.6)	(0.5)
Gain (Loss) on cash flow hedges, Tax	(0.5)	2.5	(0.5)
Total other comprehensive (loss) income, Tax	(0.5)	2.5	(0.5)
Unrealized gain (loss) on cash flow hedges, Net	0	(4.9)	0
Reclassification from AOCI to net income, Net	0.9	0.8	0.7
Gain (Loss) on cash flow hedges, Net	0.9	(4.1)	0.7
Other comprehensive income (loss), net of tax	$ 0.9	$ (4.1)	$ 0.7