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Fair Value Measurements (Details) - USD ($)
$ in Millions
Mar. 31, 2021
Dec. 31, 2020
Assets    
Assets, Fair Value Disclosure $ 893 $ 916
Liabilities    
Financial Liabilities Fair Value Disclosure 943 983
Carrying Amount [Member]    
Liabilities    
Carrying amount or fair value 15,823 13,401
Fair Value [Member]    
Liabilities    
Carrying amount or fair value 16,848 15,226
Fair Value, Inputs, Level 1 [Member]    
Assets    
Assets, Fair Value Disclosure 893 916
Liabilities    
Financial Liabilities Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member]    
Assets    
Assets, Fair Value Disclosure 0 0
Liabilities    
Financial Liabilities Fair Value Disclosure 943 983
Fair Value, Inputs, Level 3 [Member]    
Assets    
Assets, Fair Value Disclosure 0 0
Liabilities    
Financial Liabilities Fair Value Disclosure 0 0
Fair Value, Recurring [Member]    
Assets    
Corporate equities 850 873
Investments, including money market funds (1) 43 43
Fair Value, Recurring [Member] | Interest Rate Contract [Member]    
Liabilities    
Derivative liabilities 9 20
Fair Value, Recurring [Member] | Energy Related Derivative [Member]    
Liabilities    
Derivative liabilities 7 10
Fair Value, Recurring [Member] | IDS Derivative [Member]    
Liabilities    
Derivative liabilities 927 953
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]    
Assets    
Corporate equities 850 873
Investments, including money market funds (1) 43 43
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Contract [Member]    
Liabilities    
Derivative liability 0 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Energy Related Derivative [Member]    
Liabilities    
Derivative liability 0 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | IDS Derivative [Member]    
Liabilities    
Derivative liability 0 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]    
Assets    
Corporate equities 0 0
Investments, including money market funds (1) 0 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Contract [Member]    
Liabilities    
Derivative liability 9 20
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Energy Related Derivative [Member]    
Liabilities    
Derivative liability 7 10
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | IDS Derivative [Member]    
Liabilities    
Derivative liability 927 953
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]    
Assets    
Corporate equities 0 0
Investments, including money market funds (1) 0 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Contract [Member]    
Liabilities    
Derivative liability 0 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Energy Related Derivative [Member]    
Liabilities    
Derivative liability 0 0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | IDS Derivative [Member]    
Liabilities    
Derivative liability 0 0
Houston Electric [Member]    
Assets    
Assets, Fair Value Disclosure 27 26
Houston Electric [Member] | Carrying Amount [Member]    
Liabilities    
Carrying amount or fair value 5,968 5,019
Houston Electric [Member] | Fair Value [Member]    
Liabilities    
Carrying amount or fair value 6,485 5,957
Houston Electric [Member] | Fair Value, Inputs, Level 1 [Member]    
Assets    
Assets, Fair Value Disclosure 27 26
Houston Electric [Member] | Fair Value, Inputs, Level 2 [Member]    
Assets    
Assets, Fair Value Disclosure 0 0
Houston Electric [Member] | Fair Value, Inputs, Level 3 [Member]    
Assets    
Assets, Fair Value Disclosure 0 0
Houston Electric [Member] | Fair Value, Recurring [Member]    
Assets    
Investments, including money market funds (1) 27 26
Houston Electric [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]    
Assets    
Investments, including money market funds (1) 27 26
Houston Electric [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]    
Assets    
Investments, including money market funds (1) 0 0
Houston Electric [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]    
Assets    
Investments, including money market funds (1) 0 0
CERC Corp [Member]    
Assets    
Assets, Fair Value Disclosure 13 13
CERC Corp [Member] | Carrying Amount [Member]    
Liabilities    
Carrying amount or fair value 4,349 2,428
CERC Corp [Member] | Fair Value [Member]    
Liabilities    
Carrying amount or fair value 4,580 2,855
CERC Corp [Member] | Fair Value, Inputs, Level 1 [Member]    
Assets    
Assets, Fair Value Disclosure 13 13
CERC Corp [Member] | Fair Value, Inputs, Level 2 [Member]    
Assets    
Assets, Fair Value Disclosure 0 0
CERC Corp [Member] | Fair Value, Inputs, Level 3 [Member]    
Assets    
Assets, Fair Value Disclosure 0 0
CERC Corp [Member] | Fair Value, Recurring [Member]    
Assets    
Corporate equities 2 2
Investments, including money market funds (1) 11 11
CERC Corp [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]    
Assets    
Corporate equities 2 2
Investments, including money market funds (1) 11 11
CERC Corp [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]    
Assets    
Corporate equities 0 0
Investments, including money market funds (1) 0 0
CERC Corp [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]    
Assets    
Corporate equities 0 0
Investments, including money market funds (1) $ 0 $ 0