Income Taxes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jun. 05, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		27.50%	15.60%	8.50%	20.70%
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 411		$ 411
Tax Adjustments, Settlements, and Unusual Provisions				76
Income Tax Expense (Benefit)		$ 216	$ 172	$ 141	$ 626
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		45.70%	17.40%	7.70%	28.60%
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 411		$ 411
Tax Adjustments, Settlements, and Unusual Provisions				73
Income Tax Expense (Benefit)		$ 100	$ 87	41	$ 388
Internal Revenue Service (IRS) [Member]
Income Tax Additional Narrative Information [Line Items]
Income Tax Expense (Benefit)				(67)
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Income Tax Expense (Benefit)				$ (67)
ILLINOIS
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate	10.49%			9.50%
State and Local Jurisdiction [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Deferred Income Taxes				$ 66	23
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Increase (Decrease) in Income Taxes					9
Increase (Decrease) in Deferred Income Taxes				$ (26)	$ 9