Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) - Fair Value, Inputs, Level 3 [Member] - Derivative [Member] - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (108,000,000)	$ (133,000,000)
Discounted Cash Flow [Member] | Minimum [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	22.68	30.27
Discounted Cash Flow [Member] | Maximum [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	84.62	73.71
Discounted Cash Flow [Member] | Arithmetic Average [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	46.94	43.35
Commonwealth Edison Co
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (108,000,000)	$ (133,000,000)
Commonwealth Edison Co | Discounted Cash Flow [Member] | Minimum [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	22.68	30.27
Commonwealth Edison Co | Discounted Cash Flow [Member] | Maximum [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	84.62	73.71
Commonwealth Edison Co | Discounted Cash Flow [Member] | Arithmetic Average [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	46.94	43.35