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Short Term Borrowings and Long Term Debt Schedule of Debt (Details)
$ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
day
Dec. 31, 2019
USD ($)
Long-term debt:    
Unamortized Discount (Premium), Net $ 6 $ 7
Long-term Debt 11,521 14,244
Debt, Current 1,919 868
Long-term Debt, Term $ 11,521 14,244
Number of days until commercial paper maturity | day 60  
CERC Corp [Member]    
Long-term debt:    
Current $ 0  
Unamortized Discount (Premium), Net 4 11
Long-term Debt 2,428 2,546
Debt, Current 24 0
Long-term Debt, Term $ 2,428 2,546
Number of days until commercial paper maturity | day 30  
Houston Electric [Member]    
Long-term debt:    
Unamortized Discount (Premium), Net $ 14 15
Long-term Debt 4,406 4,719
Debt, Current 613 231
Long-term Debt, Term 4,406 4,719
ZENS due 2029 (2)    
Long-term debt:    
Long-Term 0 0
Current 15 19
Principal amount of debt issued $ 1,000  
Debt instrument interest rate 2.00%  
CenterPoint Energy senior notes 2.50% to 4.25% due 2021 to 2049 (3)    
Long-term debt:    
Long-Term $ (2,700) (3,200)
Current 500 0
Variable rate term loan [Member]    
Long-term debt:    
Long-Term 0 (1,000)
Current 700 0
Bonds Pollution Control Due Range 1 [Member]    
Long-term debt:    
Long-Term (68) (68)
Current 0 0
Commercial paper (4)    
Long-term debt:    
Long-Term (1,078) (1,633)
Current 0 0
Commercial paper (4) | CERC Corp [Member]    
Long-term debt:    
Long-Term (347) (377)
Current 0 0
First mortgage bonds 9.15% due 2021 | Houston Electric [Member]    
Long-term debt:    
Long-Term 0 (102)
Current $ 102 0
Debt instrument interest rate 9.15%  
Amount of debt secured by general mortgage bonds $ 102  
General mortgage bonds 1.85% to 6.95% due 2021 to 2048 | Houston Electric [Member]    
Long-term debt:    
Long-Term (3,912) (3,912)
Current 300 0
Amount of debt secured by general mortgage bonds $ 4,000  
General mortgage bonds 1.85% to 6.95% due 2021 to 2048 | Minimum [Member] | Houston Electric [Member]    
Long-term debt:    
Debt instrument interest rate 1.85%  
General mortgage bonds 1.85% to 6.95% due 2021 to 2048 | Maximum [Member] | Houston Electric [Member]    
Long-term debt:    
Debt instrument interest rate 6.95%  
System restoration bonds 4.243% due 2022 | Houston Electric [Member]    
Long-term debt:    
Long-Term $ (69) (134)
Current $ 66 62
Debt instrument interest rate 4.243%  
Transition bonds 5.234% due 2020 | Houston Electric [Member]    
Long-term debt:    
Long-Term $ 0 0
Current $ 0 29
Debt instrument interest rate 5.234%  
Transition bonds 2.161% to 3.028% due 2020 to 2024 | Houston Electric [Member]    
Long-term debt:    
Long-Term $ (467) (613)
Current $ 145 140
Transition bonds 2.161% to 3.028% due 2020 to 2024 | Maximum [Member] | Houston Electric [Member]    
Long-term debt:    
Debt instrument interest rate 3.028%  
Senior notes 3.55% to 6.625% due 2021 to 2047 | CERC Corp [Member]    
Long-term debt:    
Long-Term $ (2,100) (2,193)
Current $ 0 0
Senior notes 3.55% to 6.625% due 2021 to 2047 | Minimum [Member] | CERC Corp [Member]    
Long-term debt:    
Debt instrument interest rate 1.75%  
Senior notes 3.55% to 6.625% due 2021 to 2047 | Maximum [Member] | CERC Corp [Member]    
Long-term debt:    
Debt instrument interest rate 6.625%  
Other Debt    
Long-term debt:    
Long-Term $ (6) (18)
Current 12 18
Unamortized Debt    
Long-term debt:    
Unamortized Issuance Costs (17) (22)
Unamortized Debt | CERC Corp [Member]    
Long-term debt:    
Long-Term (15) (13)
Unamortized Debt | Houston Electric [Member]    
Long-term debt:    
Unamortized Issuance Costs (28) $ (27)
Parent Company [Member] | Bonds Pollution Control Due Range 1 [Member]    
Long-term debt:    
Long-Term $ (68)