Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 2,831	$ 2,803
Amortization of regulatory assets	434	390
Amortization of intangible assets, net	47	44
Amortization of energy contract assets and liabilities	24	14
Nuclear fuel	708	771
ARO accretion	375	371
Total depreciation, amortization and accretion	4,419	4,393
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	310	324
Provision for uncollectible accounts	130	89
Other decommissioning-related activity	(301)	(400)
Energy-related options	79	21
True-up adjustments to decoupling mechanisms and formula rates	66	72
Restructuring Costs	96
Inventory Write-down	119
Long-term incentive plan	(8)	33
Amortization of operating ROU asset	185	193
Deferred payments for legal settlements	200
Change in environmental liabilities		23
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	1,121	1,184
Amortization of regulatory assets	0	0
Amortization of intangible assets, net	40	37
Amortization of energy contract assets and liabilities	22	14
Nuclear fuel	708	771
ARO accretion	375	371
Total depreciation, amortization and accretion	2,266	2,377
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	89	98
Provision for uncollectible accounts	16	20
Other decommissioning-related activity	(301)	(400)
Energy-related options	79	21
True-up adjustments to decoupling mechanisms and formula rates	0	0
Restructuring Costs	88
Inventory Write-down	118
Amortization of operating ROU asset	135	138
Change in environmental liabilities		0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	689	661
Amortization of regulatory assets	152	106
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	841	767
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	85	70
Provision for uncollectible accounts	23	26
True-up adjustments to decoupling mechanisms and formula rates	51	80
Restructuring Costs	1
Inventory Write-down	1
Amortization of operating ROU asset	1	2
Deferred payments for legal settlements	200
Change in environmental liabilities		0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	238	225
Amortization of regulatory assets	21	22
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	259	247
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	4	9
Provision for uncollectible accounts	38	22
True-up adjustments to decoupling mechanisms and formula rates	(10)	0
Restructuring Costs	0
Inventory Write-down	1
Amortization of operating ROU asset	0	0
Change in environmental liabilities		0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	293	263
Amortization of regulatory assets	112	105
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	405	368
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	46	45
Provision for uncollectible accounts	12	5
True-up adjustments to decoupling mechanisms and formula rates	10	0
Restructuring Costs	0
Inventory Write-down	0
Amortization of operating ROU asset	23	23
Change in environmental liabilities		0
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	436	405
Amortization of regulatory assets	149	157
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	585	562
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	52	71
Provision for uncollectible accounts	41	16
True-up adjustments to decoupling mechanisms and formula rates	15	(8)
Restructuring Costs	0
Inventory Write-down	(1)
Amortization of operating ROU asset	21	26
Change in environmental liabilities		23
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	191	178
Amortization of regulatory assets	91	103
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	282	281
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	11	19
Provision for uncollectible accounts	24	7
True-up adjustments to decoupling mechanisms and formula rates	(20)	(9)
Restructuring Costs	0
Inventory Write-down	0
Amortization of operating ROU asset	5	6
Change in environmental liabilities		23
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	116	109
Amortization of regulatory assets	27	29
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	143	138
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	6	11
Provision for uncollectible accounts	15	2
True-up adjustments to decoupling mechanisms and formula rates	15	1
Restructuring Costs	0
Inventory Write-down	(1)
Amortization of operating ROU asset	6	7
Change in environmental liabilities		0
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	104	89
Amortization of regulatory assets	30	25
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	134	114
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	10	12
Provision for uncollectible accounts	2	6
True-up adjustments to decoupling mechanisms and formula rates	20	0
Restructuring Costs	0
Inventory Write-down	0
Amortization of operating ROU asset	$ 2	4
Change in environmental liabilities		$ 0