Unaudited Quarterly Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended																12 Months Ended
		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Revenues		$ 3,036		$ 2,212		$ 2,186		$ 3,155		$ 2,638		$ 2,098		$ 2,143		$ 2,735		$ 10,589		$ 9,614		$ 7,528
Operating income (loss)		167		226		187		251		308	[1]	297	[1]	240	[1]	291	[1]	831		1,136		1,023
Income (loss) available to common shareholders		$ 90		$ 153		$ (75)		$ 165		$ 1,296	[2]	$ 169	[2]	$ 135	[2]	$ 192	[2]	$ 333	[3]	$ 1,792	[3]	$ 432	[3]
Basic earnings (loss) per common share (1)		$ 0.18	[4]	$ 0.35	[4]	$ (0.17)	[4]	$ 0.38	[4]	$ 3.01	[4]	$ 0.39	[4]	$ 0.31	[4]	$ 0.45	[4]	$ 0.74		$ 4.16		$ 1.00
Diluted earnings (loss) per common share (1)		$ 0.18	[4]	$ 0.35	[4]	$ (0.17)	[4]	$ 0.38	[4]	$ 2.99	[4]	$ 0.39	[4]	$ 0.31	[4]	$ 0.44	[4]	$ 0.74		$ 4.13		$ 1.00
Net income																		$ 368		$ 1,792		$ 432
Reduction in income taxes due to tax reform																		0	[5]	1,113	[6]	0	[7]
Houston Electric [Member]
Revenues		$ 728		$ 897		$ 854		$ 755		$ 765		$ 843		$ 752		$ 638		3,234		2,998		3,059
Operating income (loss)		98		227		181		119		127	[1]	254	[1]	171	[1]	85	[1]	625		637		652
Net income		40		143		101		52		210	[2]	130	[2]	75	[2]	18	[2]	336		433		276
Reduction in income taxes due to tax reform																		$ 0	[8]	158	[9]	$ 0
CERC Corp [Member]
Revenues	[10]	2,303		1,312		1,328		2,400		1,872		1,251		1,387		2,093
Operating income (loss)	[10]	76		(7)		22		131		178	[1]	31	[1]	59	[1]	199	[1]
Income (loss) from continuing operations	[10]	35		(35)		(8)		78		469		(4)		17		102
Income (loss) from discontinued operations, net of tax	[10]	(2)		44		44		52		37		42		37		45
Net income	[10]	$ 33		$ 9		$ 36		$ 130		$ 506	[2]	$ 38	[2]	$ 54	[2]	$ 147	[2]
Reduction in income taxes due to tax reform																				$ 396

[1] Recast to reflect the adoption of ASU 2017-07. See Note 2(r) for further information.

[2] Income available to common shareholders and Net income for the fourth quarter 2017 include a reduction in income tax expense of $1,113 million, $158 million and $396 million for CenterPoint Energy, Houston Electric and CERC, respectively, due to the TCJA. See Note 15 for further discussion of the impacts of tax reform implementation.

[3] Income available to common shareholders for the year ended December 31, 2017 includes a reduction in income tax expense of $1,113 million due to tax reform. See Note 15 for further discussion of the impacts of the TCJA.

[4] Quarterly earnings (loss) per common share are based on the weighted average number of shares outstanding during the quarter, and the sum of the quarters may not equal annual earnings (loss) per common share.

[5] Recognized a $32 million deferred tax expense due to state law changes that resulted in remeasurement of state deferred taxes in those jurisdictions. Also recorded an additional $11 million valuation allowance on certain state net operating loss deferred tax assets that are no longer expected to be utilized prior to expiration after the Internal Spin. These items are partially offset by $24 million of amortization of the net regulatory EDIT liability as decreed by regulators in certain jurisdictions beginning in 2018.

[6] Recognized a $1.1 billion deferred tax benefit from the remeasurement of CenterPoint Energy’s ADFIT liability as a result of the enactment of the TCJA on December 22, 2017, which reduced the U.S. corporate income tax rate from 35% to 21%. For additional information on the 2017 impacts of the TCJA, please see the discussion following the deferred tax assets and liabilities table below.

[7] Recognized a $6 million deferred tax expense in 2016 due to Louisiana state law change and recorded an additional $3 million valuation allowance on certain state carryforwards.

[8] Recognized $9 million of amortization of the net regulatory EDIT liability as decreed by regulators in certain jurisdictions beginning in 2018.

[9] Recognized a $158 million deferred tax benefit from the remeasurement of Houston Electric’s ADFIT liability as a result of the enactment of the TCJA on December 22, 2017, which reduced the U.S. corporate income tax rate from 35% to 21%. For additional information on the 2017 impacts of the TCJA, please see the discussion following the deferred tax assets and liabilities table below.

[10] Amounts have been recast to reflect discontinued operations in all periods presented.