Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 856	$ 917
Amortization of regulatory assets	149	143
Amortization of intangible assets, net	16	15
Amortization of energy contract assets and liabilities	2
Nuclear fuel	231	261
ARO accretion	124	124
Total depreciation, amortization and accretion	1,378	1,460
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	98	106
Provision for uncollectible accounts	45	43
Other decommissioning-related activity	128	(202)
Energy-related options	6	37
Amortization of rate stabilization deferral	(54)	(6)
Discrete impacts from EIMA and FEJA	(17)	28
Long-term incentive plan	(7)	25
Amortization of operating ROU asset	51	53
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	290	392
Amortization of regulatory assets	0	0
Amortization of intangible assets, net	14	13
Amortization of energy contract assets and liabilities	2
Nuclear fuel	231	261
ARO accretion	124	123
Total depreciation, amortization and accretion	661	789
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	27	31
Provision for uncollectible accounts	4	0
Other decommissioning-related activity	128	(202)
Energy-related options	6	37
Amortization of rate stabilization deferral	0	0
Amortization of operating ROU asset	35	34
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	228	219
Amortization of regulatory assets	45	32
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	273	251
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	28	24
Provision for uncollectible accounts	7	9
Amortization of rate stabilization deferral	0	0
Discrete impacts from EIMA and FEJA	(17)	28
Amortization of operating ROU asset	0	1
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	79	74
Amortization of regulatory assets	7	7
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	86	81
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	1	2
Provision for uncollectible accounts	17	16
Amortization of rate stabilization deferral	0	0
Amortization of operating ROU asset	0	0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	97	85
Amortization of regulatory assets	46	51
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	143	136
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	15	15
Provision for uncollectible accounts	7	8
Amortization of rate stabilization deferral	(35)	0
Amortization of operating ROU asset	8	8
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	144	127
Amortization of regulatory assets	50	53
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	194	180
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	17	23
Provision for uncollectible accounts	10	10
Amortization of rate stabilization deferral	(19)	(6)
Amortization of operating ROU asset	5	9
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	64	58
Amortization of regulatory assets	31	36
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	95	94
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	3	6
Provision for uncollectible accounts	4	4
Amortization of rate stabilization deferral	(15)	(7)
Amortization of operating ROU asset	2	2
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	38	35
Amortization of regulatory assets	10	11
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	48	46
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	1	4
Provision for uncollectible accounts	3	4
Amortization of rate stabilization deferral	(4)	1
Amortization of operating ROU asset	2	2
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	34	25
Amortization of regulatory assets	9	6
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	43	31
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	3	4
Provision for uncollectible accounts	3	2
Amortization of rate stabilization deferral	0	0
Amortization of operating ROU asset	$ 1	$ 1