Income Taxes - Reconciliation to Effective Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%		21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	6.00%	12.30%		3.00%	9.30%
Qualified nuclear decommissioning trust fund income	0.50%	13.20%		9.40%	3.20%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments					2.50%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.40%)	(1.40%)		(0.80%)	(1.20%)
Plant basis differences	(1.70%)	(4.30%)		(3.90%)	(4.00%)
Production tax credits and other credits	(1.00%)	(3.00%)		(2.60%)	(2.60%)
Noncontrolling interests	(0.40%)	0.80%		(0.70%)	1.00%
Excess deferred tax amortization	(6.80%)	(10.10%)		(13.90%)	(15.80%)
Tax Settlements		(0.20%)			(5.00%)
Other	(4.80%)	(0.80%)		2.20%	0.10%
Effective income tax rate	12.40%	27.50%		13.70%	8.50%
Decrease in Unrecognized Tax Benefits is Reasonably Possible			$ 411
Tax Adjustments, Settlements, and Unusual Provisions			76
Income Tax Expense (Benefit)	$ (174)	$ (216)		$ (229)	$ (141)
Internal Revenue Service (IRS) [Member]
Increase (decrease) due to:
Income Tax Expense (Benefit)			67
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%		21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	4.40%	(10.30%)		90.20%	0.00%
Qualified nuclear decommissioning trust fund income	0.90%	47.40%		(1932.60%)	10.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments					0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.70%)	(4.50%)		130.60%	(3.20%)
Plant basis differences	0.00%	0.00%		0.00%	0.00%
Production tax credits and other credits	(1.40%)	(9.20%)		425.10%	(7.00%)
Noncontrolling interests	(0.60%)	2.90%		145.20%	3.10%
Excess deferred tax amortization	0.00%	0.00%		0.00%	0.00%
Tax Settlements		(0.70%)			(15.70%)
Other	(1.90%)	(0.90%)		(229.50%)	(0.50%)
Effective income tax rate	21.70%	45.70%		(1350.00%)	7.70%
Decrease in Unrecognized Tax Benefits is Reasonably Possible			411
Tax Adjustments, Settlements, and Unusual Provisions			73
Income Tax Expense (Benefit)	$ (177)	$ (100)		$ (108)	$ (41)
Exelon Generation Co L L C [Member] | Internal Revenue Service (IRS) [Member]
Increase (decrease) due to:
Income Tax Expense (Benefit)			$ 67
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%		21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	8.00%	8.10%		7.60%	12.70%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments					9.40%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.20%)		(0.10%)	(0.30%)
Plant basis differences	(0.80%)	(0.60%)		(0.70%)	(0.90%)
Production tax credits and other credits	(0.50%)	(0.40%)		(0.50%)	(0.40%)
Noncontrolling interests	0.00%	0.00%		0.00%	0.00%
Excess deferred tax amortization	(7.60%)	(5.60%)		(7.20%)	(11.80%)
Tax Settlements		0.00%			0.00%
Other	0.30%	1.10%		(1.30%)	2.10%
Effective income tax rate	20.30%	23.40%		18.80%	31.80%
Income Tax Expense (Benefit)	$ (56)	$ (60)		$ (141)	$ (142)
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%		21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	(4.10%)	(6.20%)		(2.60%)	(3.40%)
Qualified nuclear decommissioning trust fund income	0.00%	0.00%		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments					0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	0.00%		0.00%	0.00%
Plant basis differences	(16.20%)	(23.30%)		(12.60%)	(15.90%)
Production tax credits and other credits	0.00%	0.00%		0.00%	0.00%
Noncontrolling interests	0.00%	0.00%		0.00%	0.00%
Excess deferred tax amortization	(3.40%)	(3.80%)		(3.30%)	(3.50%)
Tax Settlements		0.00%			0.00%
Other	(0.10%)	(0.80%)		(0.20%)	(0.50%)
Effective income tax rate	(2.80%)	(13.10%)		2.30%	(2.30%)
Income Tax Expense (Benefit)	$ 3	$ 16		$ (9)	$ 7
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%		21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	(13.00%)	5.10%		(10.80%)	5.50%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments					0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)		(0.10%)	(0.10%)
Plant basis differences	(1.40%)	(1.20%)		(1.50%)	(1.80%)
Production tax credits and other credits	(0.90%)	(0.80%)		(0.90%)	(0.40%)
Noncontrolling interests	0.00%	0.00%		0.00%	0.00%
Excess deferred tax amortization	(17.30%)	(10.60%)		(16.00%)	(15.00%)
Tax Settlements		0.00%			0.00%
Other	(0.80%)	(0.30%)		(0.70%)	(0.50%)
Effective income tax rate	(12.50%)	13.10%		(9.00%)	8.70%
Income Tax Expense (Benefit)	$ 4	$ (8)		$ 24	$ (26)
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%		21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	5.00%	5.50%		4.60%	5.00%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments					0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.20%)		(0.10%)	(0.20%)
Plant basis differences	(1.30%)	(1.50%)		(1.30%)	(2.20%)
Production tax credits and other credits	(0.50%)	(0.50%)		(0.50%)	(0.30%)
Noncontrolling interests	0.00%	0.00%		0.00%	0.00%
Excess deferred tax amortization	(24.90%)	(24.90%)		(22.80%)	(45.30%)
Tax Settlements		0.00%			0.00%
Other	0.00%	0.10%		(0.30%)	(0.60%)
Effective income tax rate	(0.80%)	(0.50%)		0.60%	(22.60%)
Income Tax Expense (Benefit)	$ 2	$ 1		$ (3)	$ 77
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%		21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	3.40%	4.60%		2.50%	4.20%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments					0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	(0.10%)		0.00%	(0.10%)
Plant basis differences	(2.00%)	(2.10%)		(1.90%)	(2.40%)
Production tax credits and other credits	(0.50%)	(0.50%)		(0.50%)	(0.30%)
Noncontrolling interests	0.00%	0.00%		0.00%	0.00%
Excess deferred tax amortization	(17.60%)	(20.00%)		(17.40%)	(29.20%)
Tax Settlements		0.00%			0.00%
Other	0.10%	(0.40%)		(0.40%)	(0.80%)
Effective income tax rate	4.40%	2.50%		3.30%	(7.60%)
Income Tax Expense (Benefit)	$ (6)	$ (3)		$ (9)	$ 16
Delmarva Power and Light Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%		21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	6.40%	6.60%		6.50%	6.50%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments					0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)		(0.20%)	(0.30%)
Plant basis differences	(0.60%)	(0.40%)		(0.70%)	(0.50%)
Production tax credits and other credits	(0.40%)	(0.50%)		(0.40%)	(0.20%)
Noncontrolling interests	0.00%	0.00%		0.00%	0.00%
Excess deferred tax amortization	(19.90%)	(23.60%)		(19.70%)	(53.60%)
Tax Settlements		0.00%			0.00%
Other	(0.60%)	0.70%		(0.20%)	(1.10%)
Effective income tax rate	5.70%	3.60%		6.30%	(28.20%)
Income Tax Expense (Benefit)	$ (3)	$ (1)		$ (9)	$ 20
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%		21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	7.00%	6.90%		7.30%	6.80%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%		0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments					0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.30%)		(0.20%)	(0.50%)
Plant basis differences	(0.60%)	(1.30%)		(0.60%)	(3.70%)
Production tax credits and other credits	(0.50%)	(0.40%)		(0.50%)	(0.40%)
Noncontrolling interests	0.00%	0.00%		0.00%	0.00%
Excess deferred tax amortization	(41.40%)	(36.80%)		(36.30%)	(81.40%)
Tax Settlements		0.00%			0.00%
Other	0.80%	0.60%		0.00%	0.00%
Effective income tax rate	(13.90%)	(10.30%)		(9.30%)	(58.20%)
Income Tax Expense (Benefit)	$ 11	$ 7		$ 12	$ 39