Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total revenues	$ 693.8	$ 687.2	$ 2,067.4	$ 1,870.9
Depreciation and amortization	87.8	78.6	260.3	230.0
Total interest charges	46.1	42.9	140.4	123.2
Internally allocated interest	0.0	0.0	0.0	0.0
Provision (benefit) for income taxes	41.7	33.7	122.1	98.0
Net income from continuing operations	64.9	73.0	190.2	179.0
Income (loss) from discontinued operations, net	(11.7)	(61.9)	(67.2)	(59.4)
Net income	53.2	11.1	123.0	119.6
Total assets	8,816.9		8,816.9		$ 8,726.2
Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	648.2	668.5	1,844.9	1,847.3
Depreciation and amortization	79.0	75.4	233.8	225.9
Total interest charges	27.8	27.3	82.0	79.4
Provision (benefit) for income taxes	53.5	51.5	133.8	129.2
Net income	88.3	84.5	226.4	214.0
Total assets	7,532.5		7,532.5		7,274.3
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(2.8)	(0.4)	(7.0)	(1.5)
Depreciation and amortization	0.0	0.0	0.0	0.0
Total interest charges	(0.3)	(1.4)	(1.0)	(3.7)
Internally allocated interest	(0.3)	(1.9)	(1.0)	(3.7)
Provision (benefit) for income taxes	0.0	0.0	0.0	0.0
Net income from continuing operations	0.0	0.0	0.0	0.0
Income (loss) from discontinued operations, net	0.0	0.0	0.0	0.0
Net income	0.0	0.0	0.0	0.0
Total assets	(6,094.6)		(6,094.6)		(1,998.5)
Eliminations [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	(2.1)	(0.2)	(4.8)	(1.0)
Depreciation and amortization	0.0	0.0	0.0	0.0
Total interest charges	0.0	0.0	0.0	0.0
Provision (benefit) for income taxes	0.0	0.0	0.0	0.0
Net income	0.0	0.0	0.0	0.0
Total assets	(2.6)		(2.6)		(7.1)
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	693.8	687.2	2,067.4	1,870.9
Revenues - External [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	648.2	668.5	1,844.9	1,847.3
Revenues - External [Member] | Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	0.0	0.0	0.0	0.0
Revenues - External [Member] | Eliminations [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	0.0	0.0	0.0	0.0
Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	0.0	0.0	0.0	0.0
Sales to Affiliates [Member] | Eliminations [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	(2.8)	(0.4)	(7.0)	(1.5)
Intracompany Sales [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	0.0	0.0	0.0	0.0
Intracompany Sales [Member] | Eliminations [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	(2.1)	(0.2)	(4.8)	(1.0)
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	560.2	581.8	1,543.2	1,547.7
Depreciation and amortization	64.6	61.8	191.5	185.6
Total interest charges	24.1	23.8	71.2	69.1
Internally allocated interest	0.0	0.0	0.0	0.0
Provision (benefit) for income taxes	50.0	48.5	116.3	112.2
Net income from continuing operations	82.1	79.7	198.0	187.1
Income (loss) from discontinued operations, net	0.0	0.0	0.0	0.0
Net income	82.1	79.7	198.0	187.1
Total assets	6,804.2		6,804.2		6,565.4
Tampa Electric [Member] | Operating Segments [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	560.2	581.8	1,543.2	1,547.7
Depreciation and amortization	64.6	61.8	191.5	185.6
Total interest charges	24.1	23.8	71.2	69.1
Provision (benefit) for income taxes	50.0	48.5	116.3	112.2
Net income	82.1	79.7	198.0	187.1
Total assets	6,469.5		6,469.5		6,234.4
Tampa Electric [Member] | Revenues - External [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	559.4	581.5	1,540.8	1,546.9
Tampa Electric [Member] | Revenues - External [Member] | Operating Segments [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	560.1	581.6	1,542.9	1,547.3
Tampa Electric [Member] | Sales to Affiliates [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	0.8	0.3	2.4	0.8
Tampa Electric [Member] | Intracompany Sales [Member] | Operating Segments [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	0.1	0.2	0.3	0.4
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	90.1	86.9	306.5	300.6
Depreciation and amortization	14.4	13.6	42.3	40.3
Total interest charges	3.7	3.5	10.8	10.3
Internally allocated interest	0.0	0.0	0.0	0.0
Provision (benefit) for income taxes	3.5	3.0	17.5	17.0
Net income from continuing operations	6.2	4.8	28.4	26.9
Income (loss) from discontinued operations, net	0.0	0.0	0.0	0.0
Net income	6.2	4.8	28.4	26.9
Total assets	1,099.0		1,099.0		1,082.8
PGS [Member] | Operating Segments [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	90.1	86.9	306.5	300.6
Depreciation and amortization	14.4	13.6	42.3	40.3
Total interest charges	3.7	3.5	10.8	10.3
Provision (benefit) for income taxes	3.5	3.0	17.5	17.0
Net income	6.2	4.8	28.4	26.9
Total assets	1,065.6		1,065.6		1,047.0
PGS [Member] | Revenues - External [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	88.1	86.9	302.0	300.0
PGS [Member] | Revenues - External [Member] | Operating Segments [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Total revenues	88.1	86.9	302.0	300.0
PGS [Member] | Sales to Affiliates [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	2.0	0.0	4.5	0.6
PGS [Member] | Intracompany Sales [Member] | Operating Segments [Member] | Tampa Electric Company [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	2.0	0.0	4.5	0.6
NMGC [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	43.7	16.2	216.7	16.2
Depreciation and amortization	8.5	2.8	25.3	2.8
Total interest charges	3.2	1.1	9.8	1.1
Internally allocated interest	0.0	0.0	0.0	0.0
Provision (benefit) for income taxes	(1.9)	(0.5)	7.1	(0.5)
Net income from continuing operations	(2.8)	(0.9)	11.0	(0.9)
Income (loss) from discontinued operations, net	0.0	0.0	0.0	0.0
Net income	(2.8)	(0.9)	11.0	(0.9)
Total assets	1,188.7		1,188.7		1,237.2
NMGC [Member] | Revenues - External [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	43.7	16.2	216.7	16.2
NMGC [Member] | Sales to Affiliates [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	0.0	0.0	0.0	0.0
TECO Coal [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0.0	0.0	0.0	0.0
Depreciation and amortization	0.0	0.0	0.0	0.0
Total interest charges	0.0	0.0	0.0	0.0
Internally allocated interest	0.0	0.0	0.0	0.0
Provision (benefit) for income taxes	0.0	0.0	0.0	0.0
Net income from continuing operations	0.0	0.0	0.0	0.0
Income (loss) from discontinued operations, net	(12.1)	(64.8)	(69.6)	(65.6)
Net income	(12.1)	(64.8)	(69.6)	(65.6)
Total assets	0.0		0.0		227.7
TECO Coal [Member] | Revenues - External [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	0.0	0.0	0.0	0.0
TECO Coal [Member] | Sales to Affiliates [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	0.0	0.0	0.0	0.0
Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	2.6	2.7	8.0	7.9
Depreciation and amortization	0.3	0.4	1.2	1.3
Total interest charges	15.4	15.9	49.6	46.4
Internally allocated interest	0.3	1.9	1.0	3.7
Provision (benefit) for income taxes	(9.9)	(17.3)	(18.8)	(30.7)
Net income from continuing operations	(20.6)	(10.6)	(47.2)	(34.1)
Income (loss) from discontinued operations, net	0.4	2.9	2.4	6.2
Net income	(20.2)	(7.7)	(44.8)	(27.9)
Total assets	5,819.6		5,819.6		$ 1,611.6
Other [Member] | Revenues - External [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	2.6	2.6	7.9	7.8
Other [Member] | Sales to Affiliates [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Sales to affiliates/Intracompany sales	$ 0.0	$ 0.1	$ 0.1	$ 0.1