Short-Term Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	9 Months Ended
Feb. 18, 2011	Sep. 30, 2011	Dec. 31, 2010
Commitment fees, basis points	70
Weighted-average interest rate			0.64%
Federal funds rate plus basis points	50
Tampa Electric Co [Member]
Borrowing facility, accounts receivable	$ 150
Commitment fees, basis points	70	These credit facilities require commitment fees ranging from 7.0 to 35.0 basis points
Weighted-average interest rate			0.64%
Federal funds rate plus basis points	50

Description of the fees for amounts available, but unused under the credit facility.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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