Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			$ 3,043	$ 1,715
Amortization of regulatory assets			291	277
Amortization of intangible assets, net			29	31
Amortization of energy contract assets and liabilities			13	12
Nuclear fuel			549	459
ARO accretion			255	247
Total depreciation, amortization and accretion			4,180	2,741
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			196	203
Allowance for credit losses			100	92
Other decommissioning-related activity			(636)	(60)
Energy-related options			20	27
True-up adjustments to decoupling mechanisms and formula rates	$ 47	$ (122)	176	(55)
Long-term incentive plan			62	(10)
Amortization of operating ROU asset			83	112
Deferred payments for legal settlements				200
AFUDC - Equity	(35)	(26)	(64)	(49)
Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(176)	55
Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(64)	(49)
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			1,844	577
Amortization of regulatory assets			0	0
Amortization of intangible assets, net			25	27
Amortization of energy contract assets and liabilities			13	10
Nuclear fuel			549	459
ARO accretion			255	247
Total depreciation, amortization and accretion			2,686	1,320
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			56	58
Allowance for credit losses			46	13
Other decommissioning-related activity			(636)	(60)
Energy-related options			20	27
Long-term incentive plan			0	0
Amortization of operating ROU asset			51	80
Deferred payments for legal settlements				0
AFUDC - Equity	0	0	0	0
Exelon Generation Co L L C [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			0	0
Exelon Generation Co L L C [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			0	0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			480	458
Amortization of regulatory assets			109	89
Amortization of intangible assets, net			0	0
Amortization of energy contract assets and liabilities			0	0
Nuclear fuel			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			589	547
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			64	57
Allowance for credit losses			24	17
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	9	(25)	64	(13)
Long-term incentive plan			0	0
Amortization of operating ROU asset			1	1
Deferred payments for legal settlements				200
AFUDC - Equity	(9)	(8)	(13)	(14)
Commonwealth Edison Co [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(64)	13
Commonwealth Edison Co [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(13)	(14)
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			165	159
Amortization of regulatory assets			8	14
Amortization of intangible assets, net			0	0
Amortization of energy contract assets and liabilities			0	0
Nuclear fuel			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			173	173
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			4	3
Allowance for credit losses			17	29
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	7	4	17	5
Long-term incentive plan			0	0
Amortization of operating ROU asset			0	0
Deferred payments for legal settlements				0
AFUDC - Equity	(6)	(4)	(12)	(7)
PECO Energy Co [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(17)	(5)
PECO Energy Co [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(12)	(7)
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			215	195
Amortization of regulatory assets			78	77
Amortization of intangible assets, net			0	0
Amortization of energy contract assets and liabilities			0	0
Nuclear fuel			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			293	272
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			29	31
Allowance for credit losses			4	10
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	(10)	(37)	8	0
Long-term incentive plan			0	0
Amortization of operating ROU asset			15	15
Deferred payments for legal settlements				0
AFUDC - Equity	(7)	(6)	(14)	(10)
Baltimore Gas and Electric Company [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(8)	0
Baltimore Gas and Electric Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(14)	(10)
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			309	289
Amortization of regulatory assets			95	96
Amortization of intangible assets, net			0	0
Amortization of energy contract assets and liabilities			0	0
Nuclear fuel			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			404	385
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			24	35
Allowance for credit losses			9	22
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	41	(64)	88	(47)
Long-term incentive plan			0	0
Amortization of operating ROU asset			14	14
Deferred payments for legal settlements				0
AFUDC - Equity	(12)	(8)	(25)	(17)
Pepco Holdings LLC [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(88)	47
Pepco Holdings LLC [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(25)	(17)
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			135	126
Amortization of regulatory assets			64	60
Amortization of intangible assets, net			0	0
Amortization of energy contract assets and liabilities			0	0
Nuclear fuel			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			199	186
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			3	7
Allowance for credit losses			5	12
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	19	(13)	46	2
Long-term incentive plan			0	0
Amortization of operating ROU asset			3	3
Deferred payments for legal settlements				0
AFUDC - Equity	(10)	(6)	(20)	(13)
Potomac Electric Power Company [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(46)	(2)
Potomac Electric Power Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(20)	(13)
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			84	76
Amortization of regulatory assets			20	18
Amortization of intangible assets, net			0	0
Amortization of energy contract assets and liabilities			0	0
Nuclear fuel			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			104	94
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			1	4
Allowance for credit losses			2	8
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	10	(25)	19	(24)
Long-term incentive plan			0	0
Amortization of operating ROU asset			5	4
Deferred payments for legal settlements				0
AFUDC - Equity	(1)	(1)	(3)	(2)
Delmarva Power and Light Company [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(19)	24
Delmarva Power and Light Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(3)	(2)
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			76	69
Amortization of regulatory assets			11	17
Amortization of intangible assets, net			0	0
Amortization of energy contract assets and liabilities			0	0
Nuclear fuel			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			87	86
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			5	7
Allowance for credit losses			2	2
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	12	(26)	23	(25)
Long-term incentive plan			0	0
Amortization of operating ROU asset			2	2
Deferred payments for legal settlements				0
AFUDC - Equity	$ (1)	$ (1)	(2)	(2)
Atlantic City Electric Company [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(23)	25
Atlantic City Electric Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			$ (2)	$ (2)