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, 2022	Dec. 31, 2021
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (43,000,000)	$ (219,000,000)
Discounted Cash Flow [Member] | Minimum [Member]
Derivatives Fair Value Footnotes [Abstract]
Fair Value Inputs Forward Power Price	36.02	28.65
Discounted Cash Flow [Member] | Maximum [Member]
Derivatives Fair Value Footnotes [Abstract]
Fair Value Inputs Forward Power Price	111.10	47.10
Discounted Cash Flow [Member] | Arithmetic Average [Member]
Derivatives Fair Value Footnotes [Abstract]
Fair Value Inputs Forward Power Price	50.61	33.96
Commonwealth Edison Co [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (43,000,000)	$ (219,000,000)
Commonwealth Edison Co [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Derivatives Fair Value Footnotes [Abstract]
Fair Value Inputs Forward Power Price	36.02	28.65
Commonwealth Edison Co [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Derivatives Fair Value Footnotes [Abstract]
Fair Value Inputs Forward Power Price	111.10	47.10
Commonwealth Edison Co [Member] | Discounted Cash Flow [Member] | Arithmetic Average [Member]
Derivatives Fair Value Footnotes [Abstract]
Fair Value Inputs Forward Power Price	50.61	33.96