Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2020
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	100.00%
Minimum expectation of tax position to be realized	50.00%
Commonwealth Edison Company [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Percentage ownership of consolidated subsidiaries	99.00%
CENG [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Equity Method Investment, Ownership Percentage	50.01%
ExGen Renewables [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Equity Method Investment, Ownership Percentage	51.00%
Minimum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Equity Method Investment, Ownership Percentage	20.00%
Maximum [Member]
Significant Accounting Policies Additional Narrative Information [Line Items]
Equity Method Investment, Ownership Percentage	50.00%