Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
Total revenues	$ 599	$ 547
Total interest charges	33	34
Net income	92	77
Total assets	11,208		$ 11,048
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	599	547
Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(3)	(3)
Total interest charges	0	0
Net income	0	0
Total assets	(669)		(653)
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)	(3)
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	447	421
Total interest charges	28	30
Net income	65	59
Total assets	9,909		9,800
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	446	420
Tampa Electric [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	1	1
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	155	129
Total interest charges	5	4
Net income	27	18
Total assets	1,968		$ 1,901
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	153	127
PGS [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	$ 2	$ 2