Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 596	$ 654	$ 1,692	$ 1,820
Total interest charges	32	35	98	101
Net income	141	126	335	297
Total assets	10,763		10,763		$ 10,007
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	596	654	1,692	1,820
Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	0	0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(2)	(6)	(8)	(16)
Total interest charges	0	0	0	0
Net income	0	0	0	0
Total assets	(630)		(630)		(593)
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	(2)	(6)	(8)	(16)
Tampa Electric [Member]
Segment Reporting Information [Line Items]
Total revenues	506	559	1,381	1,492
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	506	559	1,381	1,492
Total interest charges	28	30	85	88
Net income	131	116	296	255
Total assets	9,600		9,600		9,007
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	505	558	1,378	1,489
Tampa Electric [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	1	1	3	3
PGS [Member]
Segment Reporting Information [Line Items]
Total revenues	92	101	319	344
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	92	101	319	344
Total interest charges	4	5	13	13
Net income	10	10	39	42
Total assets	1,793		1,793		$ 1,593
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	91	96	314	331
PGS [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	$ 1	$ 5	$ 5	$ 13