Segment Information - Schedule of Segment Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total revenues	$ 693.0us-gaap_Revenues	$ 578.0us-gaap_Revenues
Depreciation and amortization	85.5us-gaap_DepreciationAndAmortization	75.9us-gaap_DepreciationAndAmortization
Total interest charges	47.9us-gaap_InterestExpense	39.6us-gaap_InterestExpense
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Provision (benefit) for income taxes	39.9us-gaap_IncomeTaxExpenseBenefit	29.1us-gaap_IncomeTaxExpenseBenefit
Net income (loss) from continuing operations	63.8	48.4
Income (loss) from discontinued operations, net	(5.8)	1.7
Net income (loss)	58.0us-gaap_NetIncomeLoss	50.1us-gaap_NetIncomeLoss
Total assets	8,777.5us-gaap_Assets		8,726.2us-gaap_Assets
Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	572.1	575.5
Depreciation and amortization	76.8	75.4
Total interest charges	27.0	25.4
Provision (benefit) for income taxes	36.6	35.8
Net income (loss)	62.8	59.8
Total assets	7,320.1		7,274.3
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(2.0)	(0.5)
Depreciation and amortization	0	0
Total interest charges	(0.3)	(1.8)
Internally allocated interest	(0.3)	(1.8)
Provision (benefit) for income taxes	0	0
Net income (loss) from continuing operations	(68.9)	(48.9)
Income (loss) from discontinued operations, net	0	0
Net income (loss)	(68.9)	(48.9)
Total assets	(6,147.7)		(6,051.3)
Eliminations \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	(1.4)	(0.3)
Depreciation and amortization	0	0
Total interest charges	0	0
Provision (benefit) for income taxes	0	0
Net income (loss)	0	0
Total assets	(9.0)		(7.1)
Tampa Electric [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	450.6	453.2
Depreciation and amortization	62.9	62.1
Total interest charges	23.5	22.0
Internally allocated interest	0	0
Provision (benefit) for income taxes	27.4	26.6
Net income (loss) from continuing operations	48.2	45.2
Income (loss) from discontinued operations, net	0	0
Net income (loss)	48.2	45.2
Total assets	6,619.7		6,565.4
Tampa Electric [Member] \| Operating Segments [Member] \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	450.6	453.2
Depreciation and amortization	62.9	62.1
Total interest charges	23.5	22.0
Provision (benefit) for income taxes	27.4	26.6
Net income (loss)	48.2	45.2
Total assets	6,278.7		6,234.4
PGS [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	122.9	122.6
Depreciation and amortization	13.9	13.3
Total interest charges	3.5	3.4
Internally allocated interest	0	0
Provision (benefit) for income taxes	9.2	9.2
Net income (loss) from continuing operations	14.6	14.6
Income (loss) from discontinued operations, net	0	0
Net income (loss)	14.6	14.6
Total assets	1,085.5		1,082.8
PGS [Member] \| Operating Segments [Member] \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	122.9	122.6
Depreciation and amortization	13.9	13.3
Total interest charges	3.5	3.4
Provision (benefit) for income taxes	9.2	9.2
Net income (loss)	14.6	14.6
Total assets	1,050.4		1,047.0
NMGC [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	119.0	0
Depreciation and amortization	8.4	0
Total interest charges	3.3	0
Internally allocated interest	0	0
Provision (benefit) for income taxes	9.0	0
Net income (loss) from continuing operations	13.9	0
Income (loss) from discontinued operations, net	0	0
Net income (loss)	13.9	0
Total assets	1,207.9		1,237.2
TECO Coal [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Depreciation and amortization	0	0
Total interest charges	0	0
Internally allocated interest	0	0
Provision (benefit) for income taxes	0	0
Net income (loss) from continuing operations	0	0
Income (loss) from discontinued operations, net	(6.0)	(1.6)
Net income (loss)	(6.0)	(1.6)
Total assets	209.6		227.7
Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	2.5	2.7
Depreciation and amortization	0.3	0.5
Total interest charges	17.9	16.0
Internally allocated interest	0.3	1.8
Provision (benefit) for income taxes	(5.7)	(6.7)
Net income (loss) from continuing operations	56.0	37.5
Income (loss) from discontinued operations, net	0.2	3.3
Net income (loss)	56.2	40.8
Total assets	5,802.5		5,664.4
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	693.0	578.0
Revenues - External [Member] \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	572.1	575.5
Revenues - External [Member] \| Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Revenues - External [Member] \| Eliminations \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Revenues - External [Member] \| Tampa Electric [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	449.8	452.9
Revenues - External [Member] \| Tampa Electric [Member] \| Operating Segments [Member] \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	450.4	453.1
Revenues - External [Member] \| PGS [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	121.7	122.4
Revenues - External [Member] \| PGS [Member] \| Operating Segments [Member] \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	121.7	122.4
Revenues - External [Member] \| NMGC [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	119.0	0
Revenues - External [Member] \| TECO Coal [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Revenues - External [Member] \| Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	2.5	2.7
Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	0	0
Sales to Affiliates [Member] \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	0	0
Sales to Affiliates [Member] \| Eliminations [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	(2.0)	(0.5)
Sales to Affiliates [Member] \| Eliminations \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	(1.4)	(0.3)
Sales to Affiliates [Member] \| Tampa Electric [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	0.8	0.3
Sales to Affiliates [Member] \| Tampa Electric [Member] \| Operating Segments [Member] \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	0.2	0.1
Sales to Affiliates [Member] \| PGS [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	1.2	0.2
Sales to Affiliates [Member] \| PGS [Member] \| Operating Segments [Member] \| Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	1.2	0.2
Sales to Affiliates [Member] \| NMGC [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	0	0
Sales to Affiliates [Member] \| TECO Coal [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	0	0
Sales to Affiliates [Member] \| Other [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	$ 0	$ 0

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