Fair Value Measurements (Narrative) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Long-term debt, carrying amount	$ 3,082.2	$ 3,226.4
Long-term debt, estimated fair value	3,354.8	3,449.3
Tampa Electric Co [Member]
Long-term debt, carrying amount	1,994.7	2,069.5
Long-term debt, estimated fair value	$ 2,182.6	$ 2,217.0