Revenue - Summary of Disaggregates TEC Revenue by Major Source (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Total electric revenue	$ 593	$ 597	$ 1,563	$ 1,581
Total gas revenue	104	96	350	309
Total revenues	697	$ 693	1,913	$ 1,890
Residential [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	331		802
Total gas revenue	29		120
Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	163		435
Total gas revenue	34		115
Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	43		121
Total gas revenue	4		15
Regulatory Deferrals and Unbilled Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	(10)		13
Other [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	66		192
Total gas revenue	37		100
Tampa Electric [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	594		1,565
Total gas revenue	0		0
Total revenues	594		1,565
Tampa Electric [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	331		802
Total gas revenue	0		0
Tampa Electric [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	163		435
Total gas revenue	0		0
Tampa Electric [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	43		121
Total gas revenue	0		0
Tampa Electric [Member] | Regulatory Deferrals and Unbilled Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	(10)		13
Tampa Electric [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	67		194
Total gas revenue	0		0
PGS [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
Total gas revenue	111		368
Total revenues	111		368
PGS [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
Total gas revenue	29		120
PGS [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
Total gas revenue	34		115
PGS [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
Total gas revenue	4		15
PGS [Member] | Regulatory Deferrals and Unbilled Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
PGS [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
Total gas revenue	44		118
Eliminations [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	(1)		(2)
Total gas revenue	(7)		(18)
Total revenues	(8)		(20)
Eliminations [Member] | Residential [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
Total gas revenue	0		0
Eliminations [Member] | Commercial [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
Total gas revenue	0		0
Eliminations [Member] | Industrial [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
Total gas revenue	0		0
Eliminations [Member] | Regulatory Deferrals and Unbilled Revenue [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	0		0
Eliminations [Member] | Other [Member]
Disaggregation Of Revenue [Line Items]
Total electric revenue	(1)		(2)
Total gas revenue	$ (7)		$ (18)