Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) - Derivative [Member] - Fair Value, Inputs, Level 3 [Member] - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (133,000,000)	$ (84,000,000)
Minimum | Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Inputs Forward Power Price	30.27	34.78
Arithmetic Average [Member] | Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Inputs Forward Power Price	43.35	48.44
Maximum | Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Inputs Forward Power Price	73.71	75.71
Commonwealth Edison Co
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (133,000,000)	$ (84,000,000)
Commonwealth Edison Co | Minimum | Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Inputs Forward Power Price	30.27	34.78
Commonwealth Edison Co | Arithmetic Average [Member] | Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Inputs Forward Power Price	43.35	48.44
Commonwealth Edison Co | Maximum | Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value Inputs Forward Power Price	73.71	75.71