Short-term Debt and Credit Facilities - MEC (Details) $ in Millions	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Line of Credit Facility [Line Items]
Credit facilities	$ 10,873	$ 11,281
Tax-exempt bond support and letters of credit	(620)	(589)
Net credit facilities	9,134	8,683
MEC
Line of Credit Facility [Line Items]
Credit facilities	1,505	1,505
Tax-exempt bond support and letters of credit	(370)	(370)
Net credit facilities	1,135	1,135
Letters of credit outstanding	$ 34	$ 42
MEC | Line of credit
Line of Credit Facility [Line Items]
Debt to capitalization ratio	0.65
MEC | Commercial paper
Line of Credit Facility [Line Items]
Bank notes	$ 1,500
MEC | Unsecured credit facility, $1.5 billion, expiring June 2025 | Line of credit
Line of Credit Facility [Line Items]
Credit facilities	1,500
MEC | Unsecured 364-day credit facility, $5 million, expiring June 2023 | Line of credit
Line of Credit Facility [Line Items]
Credit facilities	$ 5