Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) - Fair Value, Inputs, Level 3 [Member] - Derivative [Member] - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (134,000,000)	$ (84,000,000)
Discounted Cash Flow [Member] | Minimum [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	30.13	34.78
Discounted Cash Flow [Member] | Maximum [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	72.72	75.71
Discounted Cash Flow [Member] | Arithmetic Average [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	42.77	48.44
Commonwealth Edison Co
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (134,000,000)	$ (84,000,000)
Commonwealth Edison Co | Discounted Cash Flow [Member] | Minimum [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	30.13	34.78
Commonwealth Edison Co | Discounted Cash Flow [Member] | Maximum [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	72.72	75.71
Commonwealth Edison Co | Discounted Cash Flow [Member] | Arithmetic Average [Member]
Derivatives, Fair Value [Line Items]
Fair Value Inputs Forward Power Price	42.77	48.44