Dispositions and Impairments (Significant Non-cash Items, Capital Expenditures, and Significant Financing Activities of Discontinued Operations) (Details) - DT Midstream - Discontinued operations, spinoff - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Activities
Depreciation and amortization	$ 82	$ 110
Deferred income taxes	57	95
Equity earnings of equity method investees	(59)	(75)
Asset (gains) losses and impairments, net	19	(4)
Investing Activities
Plant and equipment expenditures — non-utility	(60)	(440)
Financing Activities
Acquisition related deferred payment, excluding accretion	$ 0	$ (380)