Mergers and Acquisitions (CenterPoint Energy) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
		Mar. 31, 2019		Mar. 31, 2018	Dec. 31, 2018
Preliminary purchase price allocation [Abstract]
Goodwill		$ 5,129			$ 867
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets		9		$ 0
Business Combinations, Additional Disclosures [Abstract]
Revenues		3,531		3,155
Net income (loss)		169		165
Depreciation and amortization expense [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets		6	[1]	3
Vectren [Member]
Total purchase price consideration		$ 5,982
Cash to be paid per share of Vectren common stock prior to closing of the Merger		$ 72.00
Preliminary purchase price allocation [Abstract]
Cash and cash equivalents		$ 16
Other current assets		601
Property, plant and equipment, net		5,147
Identifiable intangibles		402
Regulatory assets		335
Other assets		151
Total assets acquired		6,652
Current liabilities		690
Regulatory liabilities		944
Other liabilities		891
Long-term debt		2,401
Total liabilities assumed		4,926
Net assets acquired		1,726
Goodwill	[2]	4,256			$ 0
Total purchase price consideration		5,982
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Estimated Fair Value		402
Business Combinations, Additional Disclosures [Abstract]
Revenues		473
Net income (loss)		(31)
Pro Forma Information [Abstract]
Operating revenues		3,780		3,618
Net income		185		100
Vectren [Member] | Depreciation and amortization expense [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets	[1]	3
Vectren [Member] | Operation and maintenance expense [Member]
Severance expense related to the Merger		61
Business Combinations, Additional Disclosures [Abstract]
Transaction costs		$ 8
Vectren [Member] | Operation and maintenance agreements [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Weighted Average Useful Lives		24 years
Estimated Fair Value		$ 48
Vectren [Member] | Customer Relationships [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Weighted Average Useful Lives		19 years
Estimated Fair Value		$ 229
Vectren [Member] | Construction Backlog [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Weighted Average Useful Lives		1 year
Estimated Fair Value		$ 54
Vectren [Member] | Trade Names [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Weighted Average Useful Lives		10 years
Estimated Fair Value		$ 71
Vectren [Member] | Operation and maintenance agreements and construction backlog [Member] | Non-utility cost of revenues [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets		9
Vectren [Member] | Customer relationships and trade names [Member] | Depreciation and amortization expense [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets		$ 3
Vectren [Member] | Stub period [Member]
Dividends declared per share		$ 0.41145
Dividends payable, date declared		Jan. 16, 2019
Dividends payable, date of record		Feb. 01, 2019
Vectren acquisition [Member]
Cash payments towards outstanding share-based awards		$ 78
Share-based award liability recorded		41
Incremental share-based awards expense recorded		37
Utility pipeline construction company [Member]
Total purchase price consideration		21
Preliminary purchase price allocation [Abstract]
Identifiable intangibles		8
Goodwill		6
Total purchase price consideration		21
Pro Forma Adjustment [Member] | Vectren acquisition [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets		4		18
Interest Expense				10
Pro Forma Information [Abstract]
Interest income		9
CenterPoint Energy [Member] | Pro Forma Adjustment [Member] | Vectren acquisition [Member]
Pro Forma Information [Abstract]
Merger-related expenses				28
Vectren [Member] | Pro Forma Adjustment [Member] | Vectren acquisition [Member]
Pro Forma Information [Abstract]
Merger-related expenses		$ 37		$ 56

[1] Includes $3 million of amortization expense related to intangibles acquired in the Merger. The fair value of intangible assets, and related amortization assumptions, acquired through acquisitions during the three months ended March 31, 2019, is preliminary and subject to change. See Note 3.

[2] CenterPoint Energy is currently assessing its reporting units subsequent to the Merger and the allocation of goodwill from the Merger to those reporting units. See Note 3.