Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			$ 4,505	$ 2,831
Amortization of regulatory assets			439	434
Amortization of intangible assets, net			44	47
Amortization of energy contract assets and liabilities			23	24
Nuclear fuel			810	708
ARO accretion			383	375
Total depreciation, amortization and accretion			6,204	4,419
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			304	310
Allowance for credit losses			155	130
Other decommissioning-related activity			(810)	(301)
Energy-related options			45	79
True-up adjustments to decoupling mechanisms and formula rates	$ (47)	$ (11)	129	(66)
Restructuring Costs			(67)	96
Inventory Write-down				119
Long-term incentive plan			94	(8)
Amortization of operating ROU asset			146	185
Deferred payments for legal settlements				200
AFUDC - Equity	(36)	(27)	(99)	(76)
Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(129)	66
Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(99)	(76)
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			2,698	1,121
Amortization of regulatory assets			0	0
Amortization of intangible assets, net			37	40
Amortization of energy contract assets and liabilities			23	22
Nuclear fuel			810	708
ARO accretion			383	375
Total depreciation, amortization and accretion			3,951	2,266
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			92	89
Allowance for credit losses			59	16
Other decommissioning-related activity			(810)	(301)
Energy-related options			45	79
Restructuring Costs			(75)	88
Inventory Write-down				118
Long-term incentive plan			0	0
Amortization of operating ROU asset			98	135
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			721	689
Amortization of regulatory assets			172	152
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			893	841
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			97	85
Allowance for credit losses			34	23
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	(32)	(38)	32	(51)
Restructuring Costs			1	1
Inventory Write-down				1
Long-term incentive plan			0	0
Amortization of operating ROU asset			2	1
Deferred payments for legal settlements				200
AFUDC - Equity	(10)	(7)	(23)	(22)
Commonwealth Edison Co [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(32)	51
Commonwealth Edison Co [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(23)	(22)
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			249	238
Amortization of regulatory assets			10	21
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			259	259
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			5	4
Allowance for credit losses			36	38
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	3	5	20	10
Restructuring Costs			0	0
Inventory Write-down				1
Long-term incentive plan			0	0
Amortization of operating ROU asset			0	0
Deferred payments for legal settlements				0
AFUDC - Equity	(7)	(5)	(19)	(12)
PECO Energy Co [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(20)	(10)
PECO Energy Co [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(19)	(12)
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			324	293
Amortization of regulatory assets			110	112
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			434	405
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			45	46
Allowance for credit losses			7	12
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	(24)	(9)	(17)	(10)
Restructuring Costs			0	0
Inventory Write-down				0
Long-term incentive plan			0	0
Amortization of operating ROU asset			22	23
Deferred payments for legal settlements				0
AFUDC - Equity	(7)	(6)	(21)	(16)
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			17	10
Baltimore Gas and Electric Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(21)	(16)
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			467	436
Amortization of regulatory assets			147	149
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			614	585
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			36	52
Allowance for credit losses			18	41
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	6	31	94	(15)
Restructuring Costs			1	0
Inventory Write-down				(1)
Long-term incentive plan			0	0
Amortization of operating ROU asset			21	21
Deferred payments for legal settlements				0
AFUDC - Equity	(12)	(9)	(36)	(26)
Pepco Holdings LLC [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(94)	15
Pepco Holdings LLC [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(36)	(26)
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			204	191
Amortization of regulatory assets			98	91
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			302	282
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			5	11
Allowance for credit losses			9	24
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	9	18	54	20
Restructuring Costs			0	0
Inventory Write-down				0
Long-term incentive plan			0	0
Amortization of operating ROU asset			5	5
Deferred payments for legal settlements				0
AFUDC - Equity	(9)	(7)	(30)	(20)
Potomac Electric Power Company [Member] | Other Non-Cash Activity
Other Non-Cash Operating Activities [Abstract]
True-up adjustments to decoupling mechanisms and formula rates			(54)	(20)
Potomac Electric Power Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(30)	(20)
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			126	116
Amortization of regulatory assets			31	27
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			157	143
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			2	6
Allowance for credit losses			3	15
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	(2)	8	17	(15)
Restructuring Costs			0	0
Inventory Write-down				(1)
Long-term incentive plan			0	0
Amortization of operating ROU asset			7	6
Deferred payments for legal settlements				0
AFUDC - Equity	(2)	(1)	(4)	(3)
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			(17)	15
Delmarva Power and Light Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			(4)	(3)
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			115	104
Amortization of regulatory assets			18	30
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			133	134
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			8	10
Allowance for credit losses			6	2
Other decommissioning-related activity			0	0
Energy-related options			0	0
True-up adjustments to decoupling mechanisms and formula rates	0	5	23	(20)
Restructuring Costs			0	0
Inventory Write-down				0
Long-term incentive plan			0	0
Amortization of operating ROU asset			3	2
Deferred payments for legal settlements				0
AFUDC - Equity	$ (1)	$ (1)	(2)	(3)
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)	20
Atlantic City Electric Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity			$ (2)	$ (3)