Income Taxes - MEC - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred income tax assets:
Regulatory liabilities	$ 1,248	$ 1,323
AROs	318	283
Other	629	632
Total deferred income tax assets	3,400	3,159
Valuation allowances	(142)	(187)
Total deferred income tax assets, net	3,258	2,972
Deferred income tax liabilities:
Property-related items	(12,596)	(12,244)
Regulatory assets	(1,034)	(898)
Other	(491)	(510)
Total deferred income tax liabilities	(15,695)	(15,650)
Net deferred income tax liability	(12,437)	(12,678)
Operating loss carryforwards	10,657
State
Deferred income tax liabilities:
Operating loss carryforwards	9,850
MEC
Deferred income tax assets:
Regulatory liabilities	218	194
AROs	204	191
Revenue sharing	34	87
State carryforwards	68	61
Employee benefits	25	37
Other	68	24
Total deferred income tax assets	617	594
Valuation allowances	(2)	(2)
Total deferred income tax assets, net	615	592
Deferred income tax liabilities:
Property-related items	(3,972)	(3,895)
Regulatory assets	(134)	(128)
Other	(3)	(2)
Total deferred income tax liabilities	(4,109)	(4,025)
Net deferred income tax liability	(3,494)	$ (3,433)
MEC | State
Deferred income tax liabilities:
Operating loss carryforwards	$ 1,000