Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total revenues	$ 644	$ 599	$ 1,197	$ 1,150
Total interest charges	30	26	59	54
Net income	86	76	142	139
Total assets	8,214		8,214		$ 8,083
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	644	599	1,197	1,150
Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	0	0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(2)	(2)	(4)	(7)
Total interest charges	0	0	0	0
Net income	0	0	0	0
Total assets	(500)		(500)		(465)
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)	(2)	(4)	(7)
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	542	499	985	924
Total interest charges	26	22	52	47
Net income	76	69	119	119
Total assets	7,486		7,486		7,357
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	542	499	984	923
Tampa Electric [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	0	0	1	1
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	104	102	216	233
Total interest charges	4	4	7	7
Net income	10	7	23	20
Total assets	1,228		1,228		$ 1,191
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	102	100	213	227
PGS [Member] | Operating Segments [Member] | Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	$ 2	$ 2	$ 3	$ 6