Business Acquisitions and Dispositions - Discontinued Operations (Details) - USD ($) $ in Millions		10 Months Ended	12 Months Ended
		Nov. 06, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense				$ 33	$ 1
Charge related to a voluntary retirement program			$ 51	48
Accrued capital expenditures			801	888	823
Eastern Energy Gas Holdings, LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense					1
Net income from discontinued operations	[1]		0	141	24
Charge related to a voluntary retirement program			4	4
Accrued capital expenditures			$ 30	$ 25	59
Eastern Energy Gas Holdings, LLC [Member] | East Ohio [Member] | Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenue		$ 594			729
Depreciation and amortization		73			76
Other operating expenses		399			444
Other income (expense), net		28			35
Income tax expense		26			53
Net income from discontinued operations		124			191
Capital expenditures		299			352
Charge related to a voluntary retirement program		20			0
Accrued capital expenditures		2			5
Eastern Energy Gas Holdings, LLC [Member] | Eastern Gathering and Processing, Inc. [Member] | Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenue		125			220
Depreciation and amortization		4			15
Other operating expenses		97			425
Income tax expense		7			(53)
Net income from discontinued operations		17			(167)
Capital expenditures		11			6
Impairment of assets		$ 0			$ (219)

[1] Includes income tax expense of $33 million and less than $1 million for the years ended December 31, 2019 and 2018, respectively.