Income Taxes - MEC - Components of Net Deferred Income Tax Liability (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred income tax assets:
Regulatory liabilities	$ 1,349	$ 1,420
AROs	304	304
Other	686	777
Total deferred income tax assets	3,159	3,178
Valuation allowances	(164)	(204)
Total deferred income tax assets, net	2,995	2,974
Deferred income tax liabilities:
Property-related items	(11,814)	(10,816)
Regulatory assets	(764)	(785)
Other	(478)	(327)
Total deferred income tax liabilities	(15,933)	(14,749)
Net deferred income tax liability	(12,938)	(11,775)
Operating loss carryforwards	10,210
State
Deferred income tax liabilities:
Operating loss carryforwards	9,013
MEC
Deferred income tax assets:
Regulatory liabilities	240	288
AROs	220	229
State carryforwards	55	52
Employee benefits	26	42
Other	30	40
Total deferred income tax assets	571	651
Valuation allowances	(1)	(25)
Total deferred income tax assets, net	570	626
Deferred income tax liabilities:
Property-related items	(3,843)	(3,583)
Regulatory assets	(112)	(97)
Other	(4)	0
Total deferred income tax liabilities	(3,959)	(3,680)
Net deferred income tax liability	(3,389)	$ (3,054)
MEC | State
Deferred income tax liabilities:
Operating loss carryforwards	$ 823