Goodwill and Other Intangibles (CenterPoint Energy and CERC) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Goodwill [Line Items]
Goodwill		$ 867		$ 867		$ 867
Intangible assets gross carrying amount		105		105		105
Intangible assets accumulated amortization		(36)		(36)		(31)
Net intangible assets		69		69		74
Amortization expense of intangible assets		2	$ 1	5	$ 3
Natural Gas Distribution [Member]
Goodwill [Line Items]
Goodwill		746		746		746
Energy Services [Member]
Goodwill [Line Items]
Goodwill	[1]	110		110		110
Accumulated goodwill impairment charge recorded in 2012		252		252		252
Other Operations [Member]
Goodwill [Line Items]
Goodwill		11		$ 11		$ 11
Customer Relationships [Member]
Goodwill [Line Items]
Intangible asset useful lives				15 years		15 years
Intangible assets gross carrying amount		86		$ 86		$ 86
Intangible assets accumulated amortization		(25)		(25)		(21)
Net intangible assets		61		$ 61		$ 65
Noncompete Agreements [Member]
Goodwill [Line Items]
Intangible asset useful lives				4 years		4 years
Intangible assets gross carrying amount		4		$ 4		$ 4
Intangible assets accumulated amortization		(2)		(2)		(2)
Net intangible assets		2		2		2
Other Intangible Assets [Member]
Goodwill [Line Items]
Intangible assets gross carrying amount		15		15		15
Intangible assets accumulated amortization		(9)		(9)		(8)
Net intangible assets		$ 6		$ 6		$ 7

[1] Amount presented is net of the accumulated goodwill impairment charge of $252 million recorded in 2012.