Regulatory Matters - MEC - Regulatory Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 6,644	$ 7,070
Cost of removal
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	26 years
Asset retirement obligations
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	30 years
MEC
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,079	1,119
MEC | Cost of removal
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	28 years
Regulatory liabilities	$ 411	392
MEC | Asset retirement obligations
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	30 years
Regulatory liabilities	$ 360	247
MEC | Revenue sharing mechanisms
Regulatory Liabilities [Line Items]
Regulatory liabilities	127	312
MEC | Deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 102	72
MEC | Pre-funded AFUDC on transmission MVPs
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	56 years
Regulatory liabilities	$ 32	34
MEC | Employee benefit plans
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 16	0
MEC | Unrealized gain on regulated derivatives
Regulatory Liabilities [Line Items]
Regulatory liability, amortization period	1 year
Regulatory liabilities	$ 0	31
MEC | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 31	$ 31