Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total revenues	$ 2,524	$ 2,470	$ 2,396
Depreciation and amortization	372	350	328
Total interest charges	118	119	106
Provision for income taxes	81	197	152
Net income	341	316	286
Total assets	9,155	8,364	8,083
Capital expenditures	1,109	640	727
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	2,524	2,470	2,396
Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(30)	(22)	(8)
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	(487)	(555)	(465)
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	(30)	(22)	(8)
Tampa Electric [Member]
Segment Reporting Information [Line Items]
Total revenues	2,066
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	2,066	2,054	1,965
Depreciation and amortization	312	300	268
Total interest charges	102	104	91
Provision for income taxes	65	171	130
Net income	294	273	251
Total assets	8,235	7,635	7,357
Capital expenditures	940	518	594
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	2,063	2,052	1,964
Tampa Electric [Member] | Operating Segments [Member] | Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	3	2	1
PGS [Member]
Segment Reporting Information [Line Items]
Total revenues	488
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	488	438	439
Depreciation and amortization	60	50	60
Total interest charges	16	15	15
Provision for income taxes	16	26	22
Net income	47	43	35
Total assets	1,407	1,284	1,191
Capital expenditures	169	122	133
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	461	418	432
PGS [Member] | Operating Segments [Member] | Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	$ 27	$ 20	$ 7