Mergers and Acquisitions (Details) - USD ($) $ / shares in Units, $ in Millions				12 Months Ended
		Feb. 01, 2019	Jan. 03, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Dividends declared per share				$ 1.12		$ 1.3475		$ 1.03
Total short-term borrowings				$ 0		$ 39
Goodwill				867		867
Reduction in income taxes due to tax reform				0	[1]	1,113	[2]	$ 0	[3]
CERC Corp [Member]
Total short-term borrowings	[4],[5]			0		39
Goodwill				867		867
Vectren [Member]
Total short-term borrowings				167
Long-term debt including current maturities				2,200
Vectren [Member] | Operation And Maintenance Expense [Member]
Transaction costs				28
Integration costs				$ 18
Atmos Energy Marketing [Member]
Purchase price consideration			$ 147
Goodwill			5
Operating Revenue						9,614		8,541
Net Income (1)	[6]					1,792		442
Atmos Energy Marketing [Member] | Customer Relationships [Member]
Intangibles estimated fair value			$ 25
Intangibles estimated useful life			15 years
Atmos Energy Marketing [Member] | CERC Corp [Member]
Goodwill			$ 5
Operating Revenue						6,603		5,467
Net Income (1)	[6]					745		$ 255
Reduction in income taxes due to tax reform						$ 396
Atmos Energy Marketing [Member] | CERC Corp [Member] | Customer Relationships [Member]
Intangibles estimated fair value			$ 25
Intangibles estimated useful life			15 years
Subsequent Event [Member] | Vectren [Member]
Effective date of acquisition		Feb. 01, 2019
Purchase price consideration		$ 6,000
Cash paid per share of Vectren common stock at closing of the Merger		$ 72.00
Subsequent Event [Member] | Vectren [Member] | Stub period [Member]
Dividends declared per share		$ 0.41145
Declaration Date		Jan. 16, 2019
Record Date		Feb. 01, 2019

[1] 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.

[2] 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.

[3] 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.

[4] Includes amounts due or exchangeable within one year of the date noted.

[5] Issued by CERC Corp.

[6] Net income for the year ended December 31, 2017 includes a reduction in income tax expense of $1,113 million and $396 million due to the TCJA for CenterPoint Energy and CERC, respectively. See Note 15 for further discussion of the impacts of tax reform implementation.