Significant Accounting Policies (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 8,713	$ 12,589	$ 11,836
Other comprehensive income	50	15	11
Separation of DT Midstream		(4,010)
Ending balance	10,401	8,713	12,589
AOCI including portion attributable to noncontrolling interest
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(112)	(137)
Other comprehensive income before reclassifications	5	2
Amounts reclassified from Accumulated other comprehensive loss	45	13
Other comprehensive income	50	15
Separation of DT Midstream		10
Ending balance	(62)	(112)	(137)
Net Unrealized Gain (Loss) on Derivatives
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(11)	(23)
Other comprehensive income before reclassifications	5	1
Amounts reclassified from Accumulated other comprehensive loss	2	6
Other comprehensive income	7	7
Separation of DT Midstream		5
Ending balance	(4)	(11)	(23)
Benefit Obligations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(101)	(109)
Other comprehensive income before reclassifications	0	1
Amounts reclassified from Accumulated other comprehensive loss	43	7
Other comprehensive income	43	8
Separation of DT Midstream		0
Ending balance	(58)	(101)	(109)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	0	(5)
Other comprehensive income before reclassifications	0	0
Amounts reclassified from Accumulated other comprehensive loss	0	0
Other comprehensive income	0	0
Separation of DT Midstream		5
Ending balance	$ 0	$ 0	$ (5)