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Stock-Based Incentive Compensation Plans and Employee Benefit Plans - Plan Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Savings Plan [Abstract]      
Number of Common stock held by the savings plan (in shares) 8,688,841    
Percentage of investment in common stocks (in hundredths) 8.00%    
Defined contribution plan cost $ 58 $ 58 $ 58
Postemployment Benefits [Abstract]      
Postemployment Benefits, Period Expense 3 1 2
Benefit expense related to deferred compensation plans 3 4 4
Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 2,072 2,135 2,005
Obligation to return cash received as collateral from securities lending (80) (81)  
Defined Benefits Plan, Fair Value Of Plan Assets, Excluding Investments Measured at Net Asset Value $ 1,303 $ 1,467  
Discount rate (as a percent) 2.80% 2.45%  
Contributions in 2021 $ 61 $ 86  
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]      
2022 166    
2023 168    
2024 167    
2025 167    
2026 163    
2027-2031 730    
Pension Plan | Qualified Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Contributions in 2021 53    
Expected Minimum Contributions in 2022 0    
Pension Plan | Nonqualified Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Contributions in 2021 8    
Expected Minimum Contributions in 2022 7    
Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 132 $ 134 128
Discount rate (as a percent) 2.85% 2.50%  
Contributions in 2021 $ 7 $ 10  
Expected Minimum Contributions in 2022 8    
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]      
2022 16    
2023 17    
2024 18    
2025 19    
2026 20    
2027-2031 103    
Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 400 631  
Obligation to return cash received as collateral from securities lending (80) (81)  
Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 903 836  
Obligation to return cash received as collateral from securities lending 0 0  
Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Obligation to return cash received as collateral from securities lending 0 0  
U.S. equity | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 89 76  
U.S. equity | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 89 76  
U.S. equity | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
U.S. equity | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Cash | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 26 29  
Cash | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 26 29  
Cash | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Cash | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Investment grade or above | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 833 767  
Investment grade or above | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Investment grade or above | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 833 767  
Investment grade or above | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Cash received as collateral from securities lending | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 80 81  
Cash received as collateral from securities lending | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 80 81  
Cash received as collateral from securities lending | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Cash received as collateral from securities lending | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
U.S. treasuries and government agencies | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 285 225  
U.S. treasuries and government agencies | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 285 225  
U.S. treasuries and government agencies | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
U.S. treasuries and government agencies | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Mortgage backed securities | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 7 5  
Mortgage backed securities | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Mortgage backed securities | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 7 5  
Mortgage backed securities | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Asset backed securities | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 3 3  
Asset backed securities | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Asset backed securities | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 3 3  
Asset backed securities | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Municipal bonds | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 40 43  
Municipal bonds | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Municipal bonds | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 40 43  
Municipal bonds | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Mutual funds | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 301  
Mutual funds | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 133 $ 134  
Mutual funds | International equities | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent)   14.00%  
Mutual funds | International equities | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 8.00% 7.00%  
Mutual funds | U.S. equity | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent)   55.00%  
Mutual funds | U.S. equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 20.00% 19.00%  
Mutual funds | Real estate | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent)   5.00%  
Mutual funds | Fixed income | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent)   27.00%  
Mutual funds | Fixed income | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 72.00% 74.00%  
Mutual funds | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 0 $ 301  
Mutual funds | Level 1 | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 133 134  
Mutual funds | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Mutual funds | Level 2 | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Mutual funds | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Mutual funds | Level 3 | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
International government bonds | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 20 18  
International government bonds | Level 1 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
International government bonds | Level 2 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 20 18  
International government bonds | Level 3 | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Common Collective Trust Funds | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 769 $ 668  
Common Collective Trust Funds | International equities | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 41.00% 37.00%  
Common Collective Trust Funds | U.S. equity | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 58.00% 3.00%  
Common Collective Trust Funds | Real estate | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 0.00% 1.00%  
Common Collective Trust Funds | Fixed income | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 1.00% 59.00%  
Benefit Obligation      
Postemployment Benefits [Abstract]      
Postemployment benefit obligations $ 8 $ 8  
Other non-qualified plans benefit obligations deferred compensation 40 43  
Benefit obligations related to split-dollar life insurance arrangements $ 29 32  
Minimum | U.S. equity | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 17.00%    
Minimum | U.S. equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 13.00%    
Minimum | International equity | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 9.00%    
Minimum | International equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 3.00%    
Minimum | Real estate | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 2.00%    
Minimum | Fixed income | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 54.00%    
Minimum | Fixed income | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 69.00%    
Minimum | Cash | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 0.00%    
Minimum | Cash | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 0.00%    
Maximum | U.S. equity | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 27.00%    
Maximum | U.S. equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 23.00%    
Maximum | International equity | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 19.00%    
Maximum | International equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 13.00%    
Maximum | Real estate | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 8.00%    
Maximum | Fixed income | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 64.00%    
Maximum | Fixed income | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 79.00%    
Maximum | Cash | Pension Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 2.00%    
Maximum | Cash | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 2.00%    
Common Stock | CenterPoint Energy      
Savings Plan [Abstract]      
Maximum limit of account balance in company stock (as a percent) 25.00%    
Houston Electric      
Savings Plan [Abstract]      
Defined contribution plan cost $ 20 18 18
Postemployment Benefits [Abstract]      
Postemployment Benefits, Period Expense 1 1 1
Benefit expense related to deferred compensation plans 0 1 1
Houston Electric | Pension Plan | Qualified Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Contributions in 2021 0    
Expected Minimum Contributions in 2022 0    
Houston Electric | Pension Plan | Nonqualified Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Contributions in 2021 0    
Expected Minimum Contributions in 2022 0    
Houston Electric | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 104 $ 106 101
Discount rate (as a percent) 2.85% 2.50%  
Contributions in 2021 $ 1 $ 3  
Expected Minimum Contributions in 2022 1    
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]      
2022 7    
2023 8    
2024 9    
2025 9    
2026 9    
2027-2031 48    
Houston Electric | Mutual funds | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 105 $ 106  
Houston Electric | Mutual funds | International equities | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 8.00% 8.00%  
Houston Electric | Mutual funds | U.S. equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 19.00% 18.00%  
Houston Electric | Mutual funds | Fixed income | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 73.00% 74.00%  
Houston Electric | Mutual funds | Level 1 | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 105 $ 106  
Houston Electric | Mutual funds | Level 2 | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Houston Electric | Mutual funds | Level 3 | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
Houston Electric | Benefit Obligation      
Postemployment Benefits [Abstract]      
Postemployment benefit obligations 3 3  
Other non-qualified plans benefit obligations deferred compensation 6 7  
Benefit obligations related to split-dollar life insurance arrangements $ 1 1  
Houston Electric | Minimum | U.S. equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 13.00%    
Houston Electric | Minimum | International equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 3.00%    
Houston Electric | Minimum | Fixed income | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 69.00%    
Houston Electric | Minimum | Cash | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 0.00%    
Houston Electric | Maximum | U.S. equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 23.00%    
Houston Electric | Maximum | International equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 13.00%    
Houston Electric | Maximum | Fixed income | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 79.00%    
Houston Electric | Maximum | Cash | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 2.00%    
CERC Corp      
Savings Plan [Abstract]      
Defined contribution plan cost $ 18 19 18
Postemployment Benefits [Abstract]      
Postemployment Benefits, Period Expense 2 0 1
Benefit expense related to deferred compensation plans 0 0 0
CERC Corp | Pension Plan | Qualified Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Contributions in 2021 0    
Expected Minimum Contributions in 2022 0    
CERC Corp | Pension Plan | Nonqualified Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Contributions in 2021 0    
Expected Minimum Contributions in 2022 0    
CERC Corp | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 28 $ 28 $ 27
Discount rate (as a percent) 2.85% 2.50%  
Contributions in 2021 $ 3 $ 3  
Expected Minimum Contributions in 2022 3    
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]      
2022 4    
2023 5    
2024 5    
2025 5    
2026 6    
2027-2031 30    
CERC Corp | Mutual funds | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 28 $ 28  
CERC Corp | Mutual funds | International equities | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 7.00% 7.00%  
CERC Corp | Mutual funds | U.S. equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 22.00% 21.00%  
CERC Corp | Mutual funds | Fixed income | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, actual allocation (as a percent) 71.00% 72.00%  
CERC Corp | Mutual funds | Level 1 | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value $ 28 $ 28  
CERC Corp | Mutual funds | Level 2 | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
CERC Corp | Mutual funds | Level 3 | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Plan assets, fair value 0 0  
CERC Corp | Benefit Obligation      
Postemployment Benefits [Abstract]      
Postemployment benefit obligations 5 5  
Other non-qualified plans benefit obligations deferred compensation 3 2  
Benefit obligations related to split-dollar life insurance arrangements $ 0 $ 0  
CERC Corp | Minimum | U.S. equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 15.00%    
CERC Corp | Minimum | International equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 2.00%    
CERC Corp | Minimum | Fixed income | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 68.00%    
CERC Corp | Minimum | Cash | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 0.00%    
CERC Corp | Maximum | U.S. equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 25.00%    
CERC Corp | Maximum | International equity | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 12.00%    
CERC Corp | Maximum | Fixed income | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 78.00%    
CERC Corp | Maximum | Cash | Other Postretirement Benefits Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Target allocation (as a percent) 2.00%