Unconsolidated Affiliate (CenterPoint Energy and CERC) - Schedules of Investments and Equity in Earnings (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated affiliates	$ 882		$ 882		$ 783
Equity in earnings (loss) of unconsolidated affiliates, net	67	$ 43	175	$ (1,432)
Preferred units – unconsolidated affiliate	363		363		363
Enable Midstream Partners
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated affiliates	881		881		782
Equity in earnings (loss) of unconsolidated affiliates, net	$ 67	$ 43	$ 175	$ (1,432)
Ownership percentage of equity method investment	100.00%		100.00%
Enable Midstream Partners | OGE
Schedule of Equity Method Investments [Line Items]
Ownership percentage of equity method investment	25.50%		25.50%
Enable Midstream Partners | Public unitholders
Schedule of Equity Method Investments [Line Items]
Ownership percentage of equity method investment	20.80%		20.80%
Enable Midstream Partners | Common Units
Schedule of Equity Method Investments [Line Items]
Limited partner interest units held (in shares)	435,866,139		435,866,139
Enable Midstream Partners | Common Units | OGE
Schedule of Equity Method Investments [Line Items]
Limited partner interest units held (in shares)	110,982,805		110,982,805
Enable Midstream Partners | Common Units | Public unitholders
Schedule of Equity Method Investments [Line Items]
Limited partner interest units held (in shares)	91,026,711		91,026,711
Enable Midstream Partners | Series A Preferred Units
Schedule of Equity Method Investments [Line Items]
Preferred units held (in shares)	14,520,000		14,520,000
Impairment charges or adjustments			$ 0
Enable Midstream Partners | Series A Preferred Units | OGE
Schedule of Equity Method Investments [Line Items]
Preferred units held (in shares)	0		0
Enable Midstream Partners | Series A Preferred Units | Public unitholders
Schedule of Equity Method Investments [Line Items]
Preferred units held (in shares)	0		0
Enable Midstream Partners | Variable Interest Entity, Not Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Ownership percentage of equity method investment	53.70%		53.70%
Enable Midstream Partners | Variable Interest Entity, Not Primary Beneficiary | Common Units
Schedule of Equity Method Investments [Line Items]
Limited partner interest units held (in shares)	233,856,623		233,856,623
Other
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated affiliates	$ 1		$ 1		$ 1