Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 539	$ 597
Intracompany sales	0	0
Total interest charges	33	30
Net income	64	63
Total assets	9,323		$ 9,155
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	539	597
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(6)	(6)
Intracompany sales	(6)	(6)
Total interest charges	0	0
Net income	0	0
Total assets	(571)		(487)
Eliminations [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0
Tampa Electric [Member]
Segment Reporting Information [Line Items]
Total revenues	412	461
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	412	461
Intracompany sales	1	0
Total interest charges	29	26
Net income	46	48
Total assets	8,451		8,235
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	411	461
PGS [Member]
Segment Reporting Information [Line Items]
Total revenues	133	142
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	133	142
Intracompany sales	5	6
Total interest charges	4	4
Net income	18	15
Total assets	1,443		$ 1,407
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	$ 128	$ 136