Segment Information - Schedule of Segment Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Total revenues	$ 2,272	$ 2,404	$ 2,524
Depreciation and amortization	384	377	372
Total interest charges	130	134	118
Provision for income taxes	82	77	81
Net income	424	370	341
Total assets	11,048	10,007	9,155
Capital expenditures	1,361	1,283	1,109
Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	2,272	2,404	2,524
Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	0	0	0
Eliminations [Member]
Segment Reporting Information [Line Items]
Total revenues	(10)	(22)	(30)
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	(653)	(593)	(487)
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	(10)	(22)	(30)
Tampa Electric [Member]
Segment Reporting Information [Line Items]
Total revenues	1,849	1,965	2,066
Tampa Electric [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	1,849	1,965	2,066
Depreciation and amortization	339	336	312
Total interest charges	113	117	102
Provision for income taxes	66	59	65
Net income	372	316	294
Total assets	9,800	9,007	8,235
Capital expenditures	1,028	1,055	940
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	1,845	1,961	2,063
Tampa Electric [Member] | Operating Segments [Member] | Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	4	4	3
PGS [Member]
Segment Reporting Information [Line Items]
Total revenues	433	461	488
PGS [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	433	461	488
Depreciation and amortization	45	41	60
Total interest charges	17	17	16
Provision for income taxes	16	18	16
Net income	52	54	47
Total assets	1,901	1,593	1,407
Capital expenditures	333	228	169
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]
Segment Reporting Information [Line Items]
Total revenues	427	443	461
PGS [Member] | Operating Segments [Member] | Sales to Affiliates [Member]
Segment Reporting Information [Line Items]
Sales to affiliates	$ 6	$ 18	$ 27