Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 1,522	$ 856
Amortization of regulatory assets	160	149
Amortization of intangible assets, net	15	16
Amortization of energy contract assets and liabilities	4	2
Nuclear fuel	276	231
ARO accretion	127	124
Total depreciation, amortization and accretion	2,104	1,378
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	95	98
Allowance for credit losses	85	45
Other decommissioning-related activity	(322)	128
Energy-related options	17	6
True-up adjustments to decoupling mechanisms and formula rates	(129)	(71)
Long-term incentive plan	32	(7)
Amortization of operating ROU asset	37	51
AFUDC - Equity	28	23
Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity	(28)	(23)
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	928	290
Amortization of regulatory assets	0	0
Amortization of intangible assets, net	12	14
Amortization of energy contract assets and liabilities	3	2
Nuclear fuel	276	231
ARO accretion	127	124
Total depreciation, amortization and accretion	1,346	661
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	26	27
Allowance for credit losses	34	4
Other decommissioning-related activity	(332)	128
Energy-related options	17	6
True-up adjustments to decoupling mechanisms and formula rates	0	0
Long-term incentive plan	0	0
Amortization of operating ROU asset	21	35
AFUDC - Equity	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	239	228
Amortization of regulatory assets	53	45
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	292	273
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	32	28
Allowance for credit losses	13	7
Other decommissioning-related activity	0	0
Energy-related options	0	0
True-up adjustments to decoupling mechanisms and formula rates	(54)	(17)
Long-term incentive plan	0	0
Amortization of operating ROU asset	0	0
AFUDC - Equity	4	6
Commonwealth Edison Co [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity	(4)	(6)
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	82	79
Amortization of regulatory assets	4	7
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	86	86
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	2	1
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	(10)	0
Long-term incentive plan	0	0
Amortization of operating ROU asset	0	0
AFUDC - Equity	6	3
PECO Energy Co [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity	(6)	(3)
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	106	97
Amortization of regulatory assets	46	46
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	152	143
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	14	15
Allowance for credit losses	4	7
Other decommissioning-related activity	0	0
Energy-related options	0	0
True-up adjustments to decoupling mechanisms and formula rates	(18)	(35)
Long-term incentive plan	0	0
Amortization of operating ROU asset	7	8
AFUDC - Equity	7	5
Baltimore Gas and Electric Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity	(7)	(5)
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	154	144
Amortization of regulatory assets	56	50
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	210	194
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	12	17
Allowance for credit losses	10	10
Other decommissioning-related activity	0	0
Energy-related options	0	0
True-up adjustments to decoupling mechanisms and formula rates	(46)	(19)
Long-term incentive plan	0	0
Amortization of operating ROU asset	7	5
AFUDC - Equity	11	9
Pepco Holdings LLC [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity	(11)	(9)
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	67	64
Amortization of regulatory assets	35	31
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	102	95
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	2	3
Allowance for credit losses	5	4
Other decommissioning-related activity	0	0
Energy-related options	0	0
True-up adjustments to decoupling mechanisms and formula rates	(26)	(15)
Long-term incentive plan	0	0
Amortization of operating ROU asset	1	2
AFUDC - Equity	9	6
Potomac Electric Power Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity	(9)	(6)
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	42	38
Amortization of regulatory assets	11	10
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	53	48
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	1	1
Allowance for credit losses	4	3
Other decommissioning-related activity	0	0
Energy-related options	0	0
True-up adjustments to decoupling mechanisms and formula rates	(9)	(4)
Long-term incentive plan	0	0
Amortization of operating ROU asset	3	2
AFUDC - Equity	1	1
Delmarva Power and Light Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity	(1)	(1)
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	37	34
Amortization of regulatory assets	10	9
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	47	43
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	3	3
Allowance for credit losses	1	3
Other decommissioning-related activity	0	0
Energy-related options	0	0
True-up adjustments to decoupling mechanisms and formula rates	(11)	0
Long-term incentive plan	0	0
Amortization of operating ROU asset	1	1
AFUDC - Equity	1	2
Atlantic City Electric Company [Member] | Return on borrowed funds
Other Non-Cash Operating Activities [Abstract]
AFUDC - Equity	$ (1)	$ (2)