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Segment Information - Schedule of Segment Information (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Segment Reporting Information [Line Items]          
Total revenues $ 747 $ 596 $ 2,000 $ 1,692  
Total interest charges 32 32 99 98  
Net income 149 141 362 335  
Total assets 11,796   11,796   $ 11,048
Revenues - External [Member]          
Segment Reporting Information [Line Items]          
Total revenues 747 596 2,000 1,692  
Intracompany Sales [Member]          
Segment Reporting Information [Line Items]          
Intracompany sales 0 0 0 0  
Eliminations [Member]          
Segment Reporting Information [Line Items]          
Total revenues (2) (2) (5) (8)  
Total interest charges 0 0 0 0  
Net income 0 0 0 0  
Total assets (658)   (658)   (653)
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 (2) (2) (5) (8)  
Tampa Electric [Member] | Operating Segments [Member]          
Segment Reporting Information [Line Items]          
Total revenues 634 506 1,613 1,381  
Total interest charges 27 28 84 85  
Net income 134 131 302 296  
Total assets 10,359   10,359   9,800
Tampa Electric [Member] | Operating Segments [Member] | Revenues - External [Member]          
Segment Reporting Information [Line Items]          
Total revenues 633 505 1,610 1,378  
Tampa Electric [Member] | Operating Segments [Member] | Intracompany Sales [Member]          
Segment Reporting Information [Line Items]          
Intracompany sales 1 1 3 3  
PGS [Member] | Operating Segments [Member]          
Segment Reporting Information [Line Items]          
Total revenues 115 92 392 319  
Total interest charges 5 4 15 13  
Net income 15 10 60 39  
Total assets 2,095   2,095   $ 1,901
PGS [Member] | Operating Segments [Member] | Revenues - External [Member]          
Segment Reporting Information [Line Items]          
Total revenues 114 91 390 314  
PGS [Member] | Operating Segments [Member] | Intracompany Sales [Member]          
Segment Reporting Information [Line Items]          
Intracompany sales $ 1 $ 1 $ 2 $ 5