Revenue (Deferred Revenue Activity) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Contract Liability [Roll Forward]
Beginning Balance	$ 65
Increases due to cash received or receivable, excluding amounts recognized as revenue during the period	79
Revenue recognized that was included in the deferred revenue balance at the beginning of the period	(19)
Ending Balance	$ 125
Discontinued operations, spinoff | DT Midstream
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred revenue		$ 22