Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total revenues	$ 2,470	$ 2,396	$ 2,419
Depreciation and amortization	350	328	313
Total interest charges	119	106	110
Provision for income taxes	197	152	166
Net income	316	286	276
Total assets	8,364	8,083	7,709
Capital expenditures	640	727	687
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	2,470	2,396	2,419
Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(22)	(8)	(6)
Depreciation and amortization	0	0	0
Total interest charges	0	0	0
Provision for income taxes	0	0	0
Net income	0	0	0
Total assets	(555)	(465)	(431)
Capital expenditures	0	0	0
Eliminations [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	0	0	0
Eliminations [Member] | Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	(22)	(8)	(6)
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	2,054	1,965	2,018
Depreciation and amortization	300	268	256
Total interest charges	104	91	95
Provision for income taxes	171	130	144
Net income	273	251	241
Total assets	7,635	7,357	7,004
Capital expenditures	518	594	593
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	2,052	1,964	2,018
Tampa Electric [Member] | Operating Segments [Member] | Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	2	1	0
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	438	439	407
Depreciation and amortization	50	60	57
Total interest charges	15	15	15
Provision for income taxes	26	22	22
Net income	43	35	35
Total assets	1,284	1,191	1,136
Capital expenditures	122	133	94
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	418	432	401
PGS [Member] | Operating Segments [Member] | Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	$ 20	$ 7	$ 6