Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 627	$ 619	$ 1,166	$ 1,216
Total interest charges	33	29	66	59
Net income	107	85	171	148
Total assets	9,572		9,572		$ 9,155
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	627	619	1,166	1,216
Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	0	0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(5)	(6)	(10)	(12)
Total interest charges	0	0	0	0
Net income	0	0	0	0
Total assets	(580)		(580)		(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	(5)	(6)	(10)	(12)
Tampa Electric [Member]
Segment Reporting Information [Line Items]
Total revenues	521	510	933	971
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	521	510	933	971
Total interest charges	29	25	58	51
Net income	93	74	139	121
Total assets	8,674		8,674		8,235
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	520	509	931	970
Tampa Electric [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	1	1	2	1
PGS [Member]
Segment Reporting Information [Line Items]
Total revenues	111	115	243	257
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	111	115	243	257
Total interest charges	4	4	8	8
Net income	14	11	32	27
Total assets	1,478		1,478		$ 1,407
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	107	110	235	246
PGS [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	$ 4	$ 5	$ 8	$ 11