Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Ultimate financial liability to superfund sites and former MGP sites	$ 37.5
Total rental expense and leases	8.1	10.2	11.5
TAMPA ELECTRIC CO [Member]
Ultimate financial liability to superfund sites and former MGP sites	37.5
Total rental expense and leases	2.2	2.2	2.3
Letters of credit outstanding	$ 0.7