Mergers and Acquisitions (CenterPoint Energy) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended				9 Months Ended				12 Months Ended
		Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019	Dec. 31, 2018
Dividends declared per share		$ 0.2875		$ 0.2775		$ 0.5750		$ 0.5550
Preliminary purchase price allocation [Abstract]
Goodwill		$ 5,179				$ 5,179				$ 5,179	$ 867
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets						19		$ 0
Business Combinations, Additional Disclosures [Abstract]
Revenues		2,742		$ 2,212		9,071		7,553
Net income (Loss)		270		158		634		248
Non-utility cost of revenues [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets		7	[1]	0		19	[1]	0
Depreciation and amortization expense [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets	[2]	$ 7		2		20		7
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				$ 72.00				$ 72.00
Preliminary purchase price allocation [Abstract]
Cash and cash equivalents		$ 16				$ 16				$ 16
Other current assets		598				598				598
Property, plant and equipment, net		5,146				5,146				5,146
Identifiable intangibles		322				322				322
Regulatory assets		338				338				338
Other assets		151				151				151
Total assets acquired		6,571				6,571				6,571
Current liabilities		690				690				690
Regulatory liabilities		944				944				944
Other liabilities		860				860				860
Long-term debt		2,401				2,401				2,401
Total liabilities assumed		4,895				4,895				4,895
Net assets acquired		1,676				1,676				1,676
Goodwill		4,306				4,306				4,306
Total purchase price consideration						5,982
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Estimated Fair Value						322
Business Combinations, Additional Disclosures [Abstract]
Revenues		756				1,917
Net income (Loss)		67				86
Pro Forma Information [Abstract]
Operating revenues		2,742		2,877		9,317		9,521
Net income		279		$ 212	[3]	649	[4]	282	[5]
Vectren [Member] | Depreciation and amortization expense [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Amortization of Intangible Assets	[2]					13
Vectren [Member] | Operation and maintenance expense [Member]
Severance expense related to the Merger						61
Business Combinations, Additional Disclosures [Abstract]
Business Combination, Integration Related Costs		19				$ 67
Vectren [Member] | Operation and maintenance agreements [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Weighted Average Useful Lives						24 years
Estimated Fair Value						$ 12
Vectren [Member] | Customer Relationships [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Weighted Average Useful Lives						18 years
Estimated Fair Value						$ 220
Vectren [Member] | Construction Backlog [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Weighted Average Useful Lives						1 year
Estimated Fair Value						$ 28
Vectren [Member] | Trade Names [Member]
Identifiable intangible assets preliminary purchase price allocation [Abstract]
Weighted Average Useful Lives						10 years
Estimated Fair Value						$ 62
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		7				19
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		5	[2]			$ 13
Vectren [Member] | Stub period [Member]
Dividends declared per share						$ 0.41145
Vectren acquisition [Member]
Cash payments towards outstanding share-based awards		78				$ 78				78
Share-based award liability recorded		41				41				41
Incremental share-based awards expense recorded						37
Utility pipeline construction company [Member]
Total purchase price consideration						25
Preliminary purchase price allocation [Abstract]
Identifiable intangibles		8				8				8
Goodwill		$ 6				6				6
Total purchase price consideration						25
Vectren [Member] | Pro Forma Adjustment [Member] | Vectren acquisition [Member]
Pro Forma Information [Abstract]
Merger-related expenses						$ 37		$ 18		38
CenterPoint Energy [Member] | Pro Forma Adjustment [Member] | Vectren acquisition [Member]
Pro Forma Information [Abstract]
Merger-related expenses										$ 1

[1] The fair value of intangible assets, and related amortization assumptions, acquired through acquisitions during the nine months ended September 30, 2019, is preliminary and subject to change. See Note 3.

[2] Includes $5 million and $13 million for the three and nine months ended September 30, 2019, respectively, 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 nine months ended September 30, 2019, is preliminary and subject to change. See Note 3.

[3] Pro forma net income was adjusted to exclude $18 million of Vectren Merger-related transaction costs incurred in 2018 and reflected in the historical income statements.

[4] Pro forma net income was adjusted to exclude $37 million of Vectren Merger-related transaction costs incurred in 2019.

[5] Pro forma net income was adjusted to include $38 million and $1 million, respectively, of Vectren and CenterPoint Energy Merger-related transaction costs incurred from October 1, 2018 to September 30, 2019.