Other Comprehensive Income (Other Comprehensive Income) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Unrealized gain (loss) on cash flow hedges, Gross	$ (2.1)	$ 0.9	$ 0.8	$ (0.5)
Unrealized gain (loss) on cash flow hedges, Tax	0.8	(0.2)	(0.3)	0.2
Unrealized gain (loss) on cash flow hedges, Net	(1.3)	0.7	0.5	(0.3)
Loss reclassified to net income, Gross	(0.8)	1.2	(2.3)	3.4
Loss reclassified to net income, Tax	(0.3)	(0.5)	0.9	(1.3)
Loss reclassified to net income, Net	(0.5)	0.7	(1.4)	2.1
Gain on cash flow hedges, Gross	(2.9)	2.1	(1.5)	2.9
Gain on cash flow hedges, Tax	1.1	(0.7)	0.6	(1.1)
Gain on cash flow hedges, Net	(1.8)	1.4	(0.9)	1.8
Amortization of unrecognized benefit costs and other, Gross	0.7	0.6	1.9	1.8
Amortization of unrecognized benefit costs and other, Tax	(0.3)	(0.2)	(0.7)	0.8
Amortization of unrecognized benefit costs and other, Net	0.4	0.4	1.2	2.6
Recognized benefit costs due to settlement, Gross		0		1.6
Recognized benefit costs due to settlement, Tax		0		(0.6)
Recognized benefit costs due to settlement, Net		0		1.0
Total other comprehensive income, Gross	(2.2)	2.7	0.4	6.3
Total other comprehensive income, Tax	0.8	(0.9)	(0.1)	(0.9)
Total other comprehensive income, Net	(1.4)	1.8	0.3	5.4
Tampa Electric Co [Member]
Unrealized gain (loss) on cash flow hedges, Gross	0	0	0	0
Unrealized gain (loss) on cash flow hedges, Tax	0	0	0	0
Unrealized gain (loss) on cash flow hedges, Net	0	0	0	0
Loss reclassified to net income, Gross	0.3	0.3	0.9	0.9
Loss reclassified to net income, Tax	(0.1)	(0.1)	(0.4)	(0.3)
Loss reclassified to net income, Net	0.2	0.2	0.5	0.6
Gain on cash flow hedges, Gross	0.3	0.3	0.9	0.9
Gain on cash flow hedges, Tax	(0.1)	(0.1)	(0.4)	(0.3)
Gain on cash flow hedges, Net	0.2	0.2	0.5	0.6
Total other comprehensive income, Gross	0.3	0.3	0.9	0.9
Total other comprehensive income, Tax	(0.1)	(0.1)	(0.4)	(0.3)
Total other comprehensive income, Net	$ 0.2	$ 0.2	$ 0.5	$ 0.6