Income Taxes - Reconciliation to Effective Tax Rate (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 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	1.40%	3.80%	(12.60%)	6.70%
Qualified nuclear decommissioning trust fund income	17.90%	18.80%	56.20%	(5.70%)
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments		5.30%		4.80%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	(0.60%)	(2.50%)	(1.00%)
Plant basis differences	(3.10%)	(1.60%)	(15.70%)	(3.70%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(1.90%)	(1.40%)	(11.00%)	(2.20%)
Noncontrolling interests	(0.90%)	0.10%	(2.50%)	1.10%
Excess deferred tax amortization	(10.40%)	(15.50%)	(50.90%)	(20.90%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		(1.90%)		(9.30%)
Other	(10.60%)	(0.40%)	38.50%	0.70%
Effective income tax rate	13.40%	27.60%	20.50%	(8.50%)
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 411		$ 411
Tax Adjustments, Settlements, and Unusual Provisions			76
Income Tax Expense (Benefit)	$ (74)	$ (219)	(55)	$ 75
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	(1.30%)	3.10%	5.30%	7.20%
Qualified nuclear decommissioning trust fund income	85.20%	17.30%	(18.30%)	(16.00%)
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments		0.00%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(1.80%)	(0.50%)	0.70%	(2.30%)
Plant basis differences	0.00%	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(13.00%)	(1.20%)	2.90%	(5.50%)
Noncontrolling interests	(4.20%)	0.10%	0.80%	3.20%
Excess deferred tax amortization	0.00%	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		(1.80%)		(26.10%)
Other	2.80%	0.30%	(3.90%)	(0.30%)
Effective income tax rate	88.70%	38.30%	8.50%	(18.80%)
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 411		$ 411
Tax Adjustments, Settlements, and Unusual Provisions			73
Income Tax Expense (Benefit)	$ (110)	$ (329)	70	$ 59
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%	(131.70%)	7.40%	19.10%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments		(288.30%)		22.20%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	2.90%	(0.10%)	(0.40%)
Plant basis differences	(0.70%)	2.40%	(0.60%)	(1.40%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.80%)	3.30%	(0.50%)	(0.40%)
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(7.00%)	116.00%	(7.00%)	(20.20%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%		0.00%
Other	(1.10%)	(32.30%)	(2.30%)	3.50%
Effective income tax rate	19.30%	(306.70%)	17.90%	43.40%
Income Tax Expense (Benefit)	$ (46)	$ (46)	$ (85)	$ (82)
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	(2.90%)	(9.70%)	(2.10%)	(1.60%)
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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	0.00%	0.00%	0.00%
Plant basis differences	(12.50%)	(23.60%)	(11.30%)	(11.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	0.00%	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(3.30%)	(4.80%)	(3.30%)	(3.30%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%		0.00%
Other	(0.40%)	(4.80%)	(0.10%)	(0.30%)
Effective income tax rate	1.90%	(21.90%)	4.20%	4.80%
Income Tax Expense (Benefit)	$ (2)	$ 7	$ (12)	$ (9)
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	(12.50%)	3.80%	(10.50%)	5.60%
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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.20%)	(0.10%)	(0.10%)
Plant basis differences	(2.30%)	(13.40%)	(1.60%)	(2.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(3.60%)	(1.00%)	(0.90%)	(0.20%)
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(17.50%)	(137.90%)	(15.90%)	(16.10%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%		0.00%
Other	(6.60%)	(1.70%)	(1.00%)	(0.60%)
Effective income tax rate	(21.60%)	(129.40%)	(9.00%)	7.60%
Income Tax Expense (Benefit)	$ 8	$ 22	$ 21	$ (18)
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	2.40%	(25.80%)	4.20%	4.30%
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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(2.20%)	(0.10%)	(0.20%)
Plant basis differences	(1.10%)	(44.70%)	(1.30%)	(3.50%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.80%)	(0.70%)	(0.50%)	(0.10%)
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(22.30%)	(1358.50%)	(20.80%)	(80.30%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%		0.00%
Other	(1.30%)	168.00%	(0.70%)	(1.50%)
Effective income tax rate	(2.20%)	(1242.90%)	1.80%	(60.30%)
Income Tax Expense (Benefit)	$ 3	$ 87	$ (5)	$ 76
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	(2.10%)	2.10%	1.50%	3.70%
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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	(0.10%)	0.00%	(0.10%)
Plant basis differences	(1.50%)	(3.90%)	(1.80%)	(2.70%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.70%)	(0.10%)	(0.50%)	(0.10%)
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(19.00%)	(89.00%)	(17.20%)	(41.60%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%		0.00%
Other	(1.90%)	(2.70%)	(0.80%)	(1.30%)
Effective income tax rate	(4.20%)	(72.70%)	2.20%	(21.10%)
Income Tax Expense (Benefit)	$ 3	$ 24	$ (3)	$ 19
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	7.00%	6.70%	6.60%	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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	0.50%	(0.20%)	(0.30%)
Plant basis differences	(0.70%)	(1.10%)	(0.70%)	(0.60%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.90%)	0.10%	(0.40%)	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(21.90%)	284.00%	(19.70%)	(72.90%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%		0.00%
Other	(1.10%)	(0.10%)	(0.10%)	0.80%
Effective income tax rate	3.20%	311.10%	6.50%	(45.50%)
Income Tax Expense (Benefit)	$ (1)	$ 28	$ (6)	$ 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	8.10%	7.20%	7.80%	12.40%
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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	0.30%	(0.20%)	7.20%
Plant basis differences	(0.60%)	10.00%	(0.70%)	146.20%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.60%)	0.00%	(0.50%)	0.70%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(28.20%)	174.50%	(28.30%)	2613.80%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%		0.00%
Other	(2.30%)	7.00%	(1.10%)	398.70%
Effective income tax rate	(2.80%)	220.00%	(2.00%)	3200.00%
Income Tax Expense (Benefit)	$ 1	$ 33	$ 1	$ 32