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Face (par) amount of debt instrument at time of issuance.

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Short-term Borrowings and Long-term Debt - Debt Repayments and Redemptions (Details) - USD ($)				1 Months Ended	12 Months Ended
	Dec. 30, 2021	Jun. 01, 2021	May 01, 2021	Dec. 31, 2020	Dec. 31, 2021	Jan. 15, 2021
Debt Instrument [Line Items]
Principal payments					$ 211,000,000
Senior Notes \| CERC Corp
Debt Instrument [Line Items]
Principal amount of debt issued					1,700,000,000
CNP Senior Note 3.85%
Debt Instrument [Line Items]
Outstanding debt balance				$ 500,000,000
Long-term Debt
Debt Instrument [Line Items]
Principal amount of debt issued					2,707,000,000
Long-term Debt \| CERC Corp
Debt Instrument [Line Items]
Principal amount of debt issued					300,000,000
Long-term Debt \| Houston Electric
Debt Instrument [Line Items]
Principal amount of debt issued					402,000,000
3.55% Senior Notes Due December 2021 \| Long-term Debt \| CERC Corp
Debt Instrument [Line Items]
Debt instrument, redemption price (as a percent)	100.00%
3.55% Senior Notes Due December 2021 \| Long-term Debt \| Senior Notes \| CERC Corp
Debt Instrument [Line Items]
Principal amount of debt issued					$ 300,000,000
Debt instrument interest rate (as a percent)					3.55%
9.15% First Mortgage Bonds due 2021 \| Long-term Debt \| First Mortgage Bonds \| Houston Electric
Debt Instrument [Line Items]
Principal amount of debt issued					$ 102,000,000
Debt instrument interest rate (as a percent)					9.15%
General Mortgage Bonds Due 2021 \| Long-term Debt \| Houston Electric
Debt Instrument [Line Items]
Principal amount of debt issued					$ 300,000,000
Debt instrument interest rate (as a percent)					1.85%
Debt instrument, redemption price (as a percent)			100.00%
CNP Senior Note 3.85% \| Long-term Debt
Debt Instrument [Line Items]
Debt instrument, redemption price (as a percent)				100.00%
CNP Senior Note 3.85% \| Long-term Debt \| Senior Notes
Debt Instrument [Line Items]
Principal amount of debt issued					$ 250,000,000	$ 250,000,000
Debt instrument interest rate (as a percent)					3.85%
Variable rate term loan \| Long-term Debt
Debt Instrument [Line Items]
Principal amount of debt issued					$ 700,000,000
Debt instrument interest rate (as a percent)					0.76%
Debt instrument, redemption price (as a percent)				100.00%
CNP Senior Note 3.60% \| Long-term Debt
Debt Instrument [Line Items]
Debt instrument, redemption price (as a percent)		100.00%
CNP Senior Note 3.60% \| Long-term Debt \| Senior Notes
Debt Instrument [Line Items]
Principal amount of debt issued					$ 500,000,000
Debt instrument interest rate (as a percent)					3.60%
Senior Notes 4.67% \| Long-term Debt \| Senior Notes
Debt Instrument [Line Items]
Principal amount of debt issued					$ 55,000,000
Debt instrument interest rate (as a percent)					4.67%
CNP Senior Notes 2.50% \| Long-term Debt
Debt Instrument [Line Items]
Debt instrument, redemption price (as a percent)	100.00%
CNP Senior Notes 2.50% \| Long-term Debt \| Senior Notes
Debt Instrument [Line Items]
Principal amount of debt issued					$ 500,000,000
Debt instrument interest rate (as a percent)					2.50%