Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 654	$ 697	$ 1,820	$ 1,913
Total interest charges	35	27	101	86
Net income	126	118	297	266
Total assets	9,740		9,740		$ 9,155
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	654	697	1,820	1,913
Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	0	0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(6)	(8)	(16)	(20)
Total interest charges	0	0	0	0
Net income	0	0	0	0
Total assets	(592)		(592)		(487)
Eliminations [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0	0	0
Eliminations [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	(6)	(8)	(16)	(20)
Tampa Electric [Member]
Segment Reporting Information [Line Items]
Total revenues	559	594	1,492	1,565
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	559	594	1,492	1,565
Total interest charges	30	23	88	75
Net income	116	109	255	230
Total assets	8,801		8,801		8,235
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	558	593	1,489	1,563
Tampa Electric [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	1	1	3	2
PGS [Member]
Segment Reporting Information [Line Items]
Total revenues	101	111	344	368
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	101	111	344	368
Total interest charges	5	4	13	11
Net income	10	9	42	36
Total assets	1,531		1,531		$ 1,407
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	96	104	331	350
PGS [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	$ 5	$ 7	$ 13	$ 18