Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 547	$ 539
Total interest charges	34	33
Net income	77	64
Total assets	10,236		$ 10,007
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	547	539
Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(3)	(6)
Total interest charges	0	0
Net income	0	0
Total assets	(604)		(593)
Eliminations [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Eliminations [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	(3)	(6)
Tampa Electric [Member]
Segment Reporting Information [Line Items]
Total revenues	421	412
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	421	412
Total interest charges	30	29
Net income	59	46
Total assets	9,195		9,007
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	420	411
Tampa Electric [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	1	1
PGS [Member]
Segment Reporting Information [Line Items]
Total revenues	129	133
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	129	133
Total interest charges	4	4
Net income	18	18
Total assets	1,645		$ 1,593
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	127	128
PGS [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	$ 2	$ 5