Earnings Per Share (CenterPoint Energy) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income available to common shareholders	$ 153	$ 169	$ 243	$ 496
Basic weighted average common shares outstanding	431,554,000	431,026,000	431,437,000	430,939,000
Plus: Incremental shares from assumed conversions:
Diluted weighted average common shares	434,891,000	434,086,000	434,774,000	433,999,000
Basic earnings per common share
Basic earnings per common share	$ 0.35	$ 0.39	$ 0.56	$ 1.15
Diluted earnings per common share
Diluted earnings per common share	$ 0.35	$ 0.39	$ 0.56	$ 1.14
Restricted Stock [Member]
Plus: Incremental shares from assumed conversions:
Restricted stock	3,337,000	3,060,000	3,337,000	3,060,000

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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