Long-Term Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended			1 Months Ended	3 Months Ended	7 Months Ended	12 Months Ended			22 Months Ended				12 Months Ended		9 Months Ended	48 Months Ended	57 Months Ended			3 Months Ended		3 Months Ended	1 Months Ended		3 Months Ended	22 Months Ended
	Feb. 15, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Feb. 15, 2013 TAMPA ELECTRIC CO [Member]	Dec. 31, 2012 TAMPA ELECTRIC CO [Member]	Dec. 31, 2012 TAMPA ELECTRIC CO [Member]	Dec. 31, 2012 TAMPA ELECTRIC CO [Member]	Dec. 31, 2011 TAMPA ELECTRIC CO [Member]	Dec. 31, 2010 TAMPA ELECTRIC CO [Member]	Dec. 31, 2012 TAMPA ELECTRIC CO [Member]	Sep. 30, 2012 TAMPA ELECTRIC CO [Member]	Sep. 28, 2012 TAMPA ELECTRIC CO [Member]	Jun. 05, 2012 TAMPA ELECTRIC CO [Member]	Dec. 19, 2012 San Jose [Member]	Dec. 31, 2012 6.75% Notes due 2015 [Member]	Dec. 31, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member]	Mar. 15, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member]	Dec. 31, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member]	Dec. 31, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member] Held Bonds [Member]	Sep. 30, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member] TAMPA ELECTRIC CO [Member]	Dec. 31, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member] TAMPA ELECTRIC CO [Member] 2013 [Member]	Sep. 30, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member] TAMPA ELECTRIC CO [Member] 2013 [Member]	Dec. 31, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member] TAMPA ELECTRIC CO [Member] 2023 [Member]	Sep. 30, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member] Five Point One Percentage Refunding Bonds [Member] TAMPA ELECTRIC CO [Member] 2013 [Member]	Sep. 30, 2012 HCIDA Pollution Control Revenue Refunding Bonds, Series 2002 [Member] Five Point Five Percentage Refunding Bonds [Member] TAMPA ELECTRIC CO [Member] 2023 [Member]	Mar. 01, 2011 PCIDA Bonds [Member]	Dec. 31, 2012 PCIDA Bonds [Member]
Debt Instrument [Line Items]
Long-term debt, carrying amount		$ 2,975.4	$ 3,075.8			$ 1,702.5	$ 1,702.5	$ 1,702.5			$ 1,702.5
Estimated fair value		3,439.4	3,432.9
Principal amounts of notes redeemed												147.1				8.8					147.1
Redemption price of notes																1,141.86
Aggregate principal amount issued													250.0	300.0		1,000.0
Loss on debt extinguishment		(1.2)	0	(54.6)												1.2
Redeemable principal amount percentage																							100.00%
Purchase in lieu of redemption		650.4	153.6	797.2				608.0	78.8	3.7	75.0				25.3		86.0		20.0	181.0					60.7	86.4		75.0
Interest at the initial term rate per annum						2.60%	4.10%											5.00%				5.10%		5.50%			1.50%
Issuance of notes, maturity year						Jan. 01, 2022	Jan. 01, 2042
Debt Instrument Principal amount Market Price Percentage						99.878%	99.724%
Proceeds from notes net of issuance						$ 247.7	$ 296.2
Libor interest rate	52.5 basis points				52.5 basis points	15	25