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v3.25.3

Short-term Borrowings and Long-term Debt - Narrative (Details) $ / shares in Units, $ in Millions |  |  |  |  |  | 1 Months Ended | 9 Months Ended |  |
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Jul. 31, 2025 USD ($) | Jul. 28, 2025 $ / shares | Jul. 01, 2025 USD ($) | Jan. 31, 2025 USD ($) | Jan. 29, 2025 | Aug. 31, 2025 USD ($) | Jul. 24, 2025 USD ($) | Jun. 30, 2025 USD ($) | May 31, 2025 USD ($) | Mar. 31, 2025 USD ($) | Feb. 28, 2025 USD ($) | Sep. 30, 2025 USD ($) shares | Jun. 20, 2025 USD ($) | Apr. 30, 2025 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset, authorized issuance costs |  |  |  |  |  |  |  |  |  |  |  |  | $ 401.5 |
Credit agreement term (in years) |  |  |  |  | 1 year |  |  |  |  |  |  |  |  |
CERC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain from early extinguishment of debt |  |  |  |  |  |  |  |  |  |  |  | $ 9.0 |  |
Parent Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain from early extinguishment of debt |  |  |  |  |  |  |  |  |  |  |  | $ 36.0 |  |
SIGECO |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of property additions (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 70.00% |  |
Outstanding debt balance |  |  |  |  |  |  |  |  |  |  |  | $ 1,300.0 |  |
Additional debt issuable |  |  |  |  |  |  |  |  |  |  |  | 944.0 |  |
Houston Electric |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory asset, authorized issuance costs |  |  |  |  |  |  |  |  |  |  |  | 401.5 |  |
Additional first mortgage bonds and general mortgage bonds that could be issued |  |  |  |  |  |  |  |  |  |  |  | $ 4,300.0 |  |
Houston Electric | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Securitiztion bonds interest rate (in percent) |  |  |  |  |  |  |  |  |  |  |  | 4.255% |  |
Houston Electric | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Securitiztion bonds interest rate (in percent) |  |  |  |  |  |  |  |  |  |  |  | 4.826% |  |
Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal amount repurchased |  |  |  |  |  |  |  |  | $ 1,000.0 |  |  |  |  |
Senior Notes | Parent Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of cancelled debt |  |  |  |  |  |  |  |  | 634.0 |  |  |  |  |
Senior Notes | CERC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of cancelled debt |  |  |  |  |  |  |  |  | $ 415.0 |  |  |  |  |
General Mortgage Bonds, 2.35% to 6.95%, Due 2026 to 2053 | Houston Electric |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Secured debt |  |  |  |  |  |  |  |  |  |  |  | $ 9,600.0 |  |
Bonds Pollution Control Due Range 1 | Houston Electric |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Secured debt |  |  |  |  |  |  |  |  |  |  |  | $ 68.0 |  |
Percentage of property additions (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 70.00% |  |
5.69% First Mortgage Bonds, Series 2025A | First Mortgage Bonds | SIGECO |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal |  |  |  | $ 165.0 |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  |  | 5.69% |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of long-term debt and capital securities, net |  |  |  | $ 164.0 |  |  |  |  |  |  |  |  |  |
General Mortgage Bonds 5.15% Due 2034 | General Mortgage Bonds | Houston Electric |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal |  |  |  |  |  |  |  |  |  |  | $ 500.0 |  |  |
Annual interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  | 4.80% |  |  |
Proceeds from issuance of long-term debt and capital securities, net |  |  |  |  |  |  |  |  |  |  | $ 495.0 |  |  |
5.09%, Series 2025B, Tranche A Due 2031 | First Mortgage Bonds | SIGECO | Long-term Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal |  |  | $ 100.0 |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  | 5.09% |  |  |  |  |  |  |  |  |  |  |
5.52%, Series 2025B, Tranche A Due 2035 | First Mortgage Bonds | SIGECO | Long-term Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal |  |  | $ 105.0 |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  | 5.52% |  |  |  |  |  |  |  |  |  |  |
5.77%, Series 2025C, Tranche A Due 2040 | First Mortgage Bonds | SIGECO | Long-term Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal |  |  | $ 45.0 |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  | 5.77% |  |  |  |  |  |  |  |  |  |  |
Number of business days |  |  | 5 days |  |  |  |  |  |  |  |  |  |  |
6.18%, Series 2025C, Tranche B Due 2055 | First Mortgage Bonds | SIGECO | Long-term Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal |  |  | $ 100.0 |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  | 6.18% |  |  |  |  |  |  |  |  |  |  |
Series 2025B Bonds | SIGECO | Long-term Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal |  |  | $ 205.0 |  |  |  |  |  |  |  |  |  |  |
4.95%, General Mortgage Bonds, Series AQ, due 2035 | General Mortgage Bonds | Houston Electric | Long-term Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal |  |  |  |  |  | $ 600.0 |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  |  |  |  | 4.95% |  |  |  |  |  |  |  |
Proceeds from issuance of long-term debt and capital securities, net |  |  |  |  |  | $ 592.0 |  |  |  |  |  |  |  |
Convertible Senior Notes, Due 2028 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, convertible, conversion ratio |  | 21.4477 |  |  |  |  |  |  |  |  |  |  |  |
Conversion price percentage |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |
Convertible Senior Notes, Due 2028 | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, convertible, conversion ratio |  |  |  |  |  |  |  |  |  |  |  | 26.8096 |  |
Debt instrument, convertible, number of equity instruments (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  | 26,809,600 |  |
Convertible Senior Notes, Due 2028 | Convertible Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal | $ 1,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) | 3.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of long-term debt and capital securities, net | $ 987.0 |  |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, convertible, conversion price (in dollar per shares) | $ / shares |  | $ 46.63 |  |  |  |  |  |  |  |  |  |  |  |
Debt instrument, redemption price, percentage |  | 100.00% |  |  |  |  |  |  |  |  |  |  |  |
Medium Term Notes, Series F, Due 2028 | CERC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  |  |  |  |  |  |  |  | 6.36% |  |  |  |
Principal amount repurchased |  |  |  |  |  |  |  |  |  | $ 10.0 |  |  |  |
Debt instrument, redemption price, percentage of principal amount redeemed |  |  |  |  |  |  |  |  |  | 104.80% |  |  |  |
Senior Notes Due 2026 to 2031 | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash tender offers |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 600.0
Senior Notes Due 2026 to 2031 | Senior Notes | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.65%
Senior Notes Due 2026 to 2031 | Senior Notes | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.40%
Senior Notes Due 2028 to 2047 | Senior Notes | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.10%
Senior Notes Due 2028 to 2047 | Senior Notes | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.40%
Senior Notes Due 2028 to 2047 | Senior Notes | CERC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash tender offers |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 400.0
Medium Term Notes, Series E, Due 2025 | CERC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  |  |  |  |  |  | 6.53% |  |  |  |  |  |
Principal amount repurchased |  |  |  |  |  |  |  | $ 10.0 |  |  |  |  |  |
Debt instrument, redemption price, percentage of principal amount redeemed |  |  |  |  |  |  |  | 100.00% |  |  |  |  |  |
First Mortgage Bonds 3.45% Due 2025 | First Mortgage Bonds | SIGECO | Long-term Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal |  |  |  |  |  |  | $ 41.0 |  |  |  |  |  |  |
Annual interest rate (as a percent) |  |  |  |  |  |  | 3.45% |  |  |  |  |  |  |
Debt instrument, redemption price, percentage |  |  |  |  |  |  | 100.00% |  |  |  |  |  |  |

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