Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 1,715	$ 1,859
Amortization of regulatory assets	277	266
Amortization of intangible assets, net	31	29
Amortization of energy contract assets and liabilities	12	5
Nuclear fuel	459	513
ARO accretion	247	250
Total depreciation, amortization and accretion	2,741	2,922
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	203	212
Provision for uncollectible accounts	92	45
Other decommissioning-related activity	(60)	(260)
Energy-related options	27	43
True-up adjustments to decoupling mechanisms and formula rates	55	14
Long-term incentive plan	(10)	35
Amortization of operating ROU asset	112	115
Deferred payments for legal settlements	200
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	577	789
Amortization of regulatory assets	0	0
Amortization of intangible assets, net	27	25
Amortization of energy contract assets and liabilities	10	5
Nuclear fuel	459	513
ARO accretion	247	248
Total depreciation, amortization and accretion	1,320	1,580
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	58	62
Provision for uncollectible accounts	13	12
Other decommissioning-related activity	(60)	(261)
Energy-related options	27	43
True-up adjustments to decoupling mechanisms and formula rates	0	0
Amortization of operating ROU asset	80	78
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	458	439
Amortization of regulatory assets	89	69
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	547	508
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	57	47
Provision for uncollectible accounts	17	16
True-up adjustments to decoupling mechanisms and formula rates	13	24
Amortization of operating ROU asset	1	1
Deferred payments for legal settlements	200
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	159	149
Amortization of regulatory assets	14	15
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	173	164
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	3	5
Provision for uncollectible accounts	29	10
True-up adjustments to decoupling mechanisms and formula rates	(5)	0
Amortization of operating ROU asset	0	0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	195	173
Amortization of regulatory assets	77	79
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	272	252
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	31	29
Provision for uncollectible accounts	10	4
True-up adjustments to decoupling mechanisms and formula rates	0	0
Amortization of operating ROU asset	15	15
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	289	266
Amortization of regulatory assets	96	103
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	385	369
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	35	48
Provision for uncollectible accounts	22	3
True-up adjustments to decoupling mechanisms and formula rates	47	(10)
Amortization of operating ROU asset	14	17
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	126	117
Amortization of regulatory assets	60	69
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	186	186
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	7	12
Provision for uncollectible accounts	12	2
True-up adjustments to decoupling mechanisms and formula rates	(2)	(8)
Amortization of operating ROU asset	3	4
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	76	71
Amortization of regulatory assets	18	20
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	94	91
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	4	8
Provision for uncollectible accounts	8	1
True-up adjustments to decoupling mechanisms and formula rates	24	(2)
Amortization of operating ROU asset	4	5
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	69	57
Amortization of regulatory assets	17	14
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	86	71
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	7	8
Provision for uncollectible accounts	2	0
True-up adjustments to decoupling mechanisms and formula rates	25	0
Amortization of operating ROU asset	$ 2	$ 2