Fair Value Measurements (Narrative) (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Long-term debt, carrying amount	$ 3,076.1	$ 3,226.4
Long-term debt, estimated fair value	3,450.7	3,449.3
Tampa Electric Co [Member]
Long-term debt, carrying amount	1,991.2	2,069.5
Long-term debt, estimated fair value	$ 2,291.4	$ 2,217.0