Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total revenues	$ 693	$ 689	$ 1,890	$ 1,839
Total interest charges	30	26	89	80
Net income	106	100	248	239
Total assets	8,306		8,306		$ 8,083
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	693	689	1,890	1,839
Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	0	0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(15)	(1)	(19)	(8)
Total interest charges	0	0	0	0
Net income	0	0	0	0
Total assets	(491)		(491)		(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	(15)	(1)	(19)	(8)
Tampa Electric [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	598	586	1,583	1,510
Total interest charges	26	22	78	69
Net income	98	94	217	213
Total assets	7,544		7,544		7,357
Tampa Electric [Member] \| Operating Segments [Member] \| Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	597	586	1,581	1,509
Tampa Electric [Member] \| Operating Segments [Member] \| Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	1	0	2	1
PGS [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	110	104	326	337
Total interest charges	4	4	11	11
Net income	8	6	31	26
Total assets	1,253		1,253		$ 1,191
PGS [Member] \| Operating Segments [Member] \| Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	96	103	309	330
PGS [Member] \| Operating Segments [Member] \| Intracompany Sales [Member]
Segment Reporting Information [Line Items]
Intracompany sales	$ 14	$ 1	$ 17	$ 7

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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