Fair Value Measurements - Schedule of Assets and Liabilities Measured On Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Assets
Equity securities	$ 1,439	$ 873
Investments, including money market funds	42	43
Natural gas derivatives	14	0
Total assets	1,495	916
Liabilities
Total liabilities	917	983
Indexed debt securities derivative
Liabilities
Derivative Liability	903	953
Interest rate derivatives
Liabilities
Derivative Liability	14	20
Natural gas derivatives
Liabilities
Derivative Liability	0	10
Level 1
Assets
Equity securities	1,439	873
Investments, including money market funds	42	43
Natural gas derivatives	0	0
Total assets	1,481	916
Liabilities
Total liabilities	0	0
Level 1 \| Indexed debt securities derivative
Liabilities
Derivative Liability	0	0
Level 1 \| Interest rate derivatives
Liabilities
Derivative Liability	0	0
Level 1 \| Natural gas derivatives
Liabilities
Derivative Liability	0	0
Level 2
Assets
Equity securities	0	0
Investments, including money market funds	0	0
Natural gas derivatives	14	0
Total assets	14	0
Liabilities
Total liabilities	917	983
Level 2 \| Indexed debt securities derivative
Liabilities
Derivative Liability	903	953
Level 2 \| Interest rate derivatives
Liabilities
Derivative Liability	14	20
Level 2 \| Natural gas derivatives
Liabilities
Derivative Liability	0	10
Level 3
Assets
Equity securities	0	0
Investments, including money market funds	0	0
Natural gas derivatives	0	0
Total assets	0	0
Liabilities
Total liabilities	0	0
Level 3 \| Indexed debt securities derivative
Liabilities
Derivative Liability	0	0
Level 3 \| Interest rate derivatives
Liabilities
Derivative Liability	0	0
Level 3 \| Natural gas derivatives
Liabilities
Derivative Liability	0	0
Houston Electric
Assets
Investments, including money market funds	27	26
Total assets	27	26
Houston Electric \| Level 1
Assets
Investments, including money market funds	27	26
Total assets	27	26
Houston Electric \| Level 2
Assets
Investments, including money market funds	0	0
Total assets	0	0
Houston Electric \| Level 3
Assets
Investments, including money market funds	0	0
Total assets	0	0
CERC Corp
Assets
Investments, including money market funds	14	13
Total assets	14	13
CERC Corp \| Level 1
Assets
Investments, including money market funds	14	13
Total assets	14	13
CERC Corp \| Level 2
Assets
Investments, including money market funds	0	0
Total assets	0	0
CERC Corp \| Level 3
Assets
Investments, including money market funds	0	0
Total assets	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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