Significant Accounting Policies (Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 12,589	$ 11,836	$ 10,717
Other comprehensive income (loss)	15	11	(3)
Separation of DT Midstream	(4,010)
Ending balance	8,713	12,589	11,836
AOCI including portion attributable to noncontrolling interest
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(137)	(148)
Other comprehensive income (loss) before reclassifications	2	(4)
Amounts reclassified from Accumulated other comprehensive loss	13	15
Other comprehensive income (loss)	15	11
Separation of DT Midstream	10
Ending balance	(112)	(137)	(148)
Net Unrealized Gain (Loss) on Derivatives
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(23)	(25)
Other comprehensive income (loss) before reclassifications	1	(3)
Amounts reclassified from Accumulated other comprehensive loss	6	5
Other comprehensive income (loss)	7	2
Separation of DT Midstream	5
Ending balance	(11)	(23)	(25)
Benefit Obligations
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(109)	(117)
Other comprehensive income (loss) before reclassifications	1	(2)
Amounts reclassified from Accumulated other comprehensive loss	7	10
Other comprehensive income (loss)	8	8
Separation of DT Midstream	0
Ending balance	(101)	(109)	(117)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(5)	(6)
Other comprehensive income (loss) before reclassifications	0	1
Amounts reclassified from Accumulated other comprehensive loss	0	0
Other comprehensive income (loss)	0	1
Separation of DT Midstream	5
Ending balance	$ 0	$ (5)	$ (6)