Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	$ 1,859	$ 1,873
Amortization of regulatory assets	266	278
Amortization of intangible assets, net	29	28
Amortization of energy contract assets and liabilities	5	10
Nuclear fuel	513	569
ARO accretion	250	242
Total depreciation, amortization and accretion	2,922	3,000
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	212	290
Provision for uncollectible accounts	45	77
Other decommissioning-related activity	(260)	(61)
Energy-related options	43	(7)
Amortization of rate stabilization deferral	(10)	13
Discrete impacts from EIMA and FEJA	24	14
Long-term incentive plan	35	51
Amortization of operating ROU asset	115
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	789	890
Amortization of regulatory assets	0	0
Amortization of intangible assets, net	25	24
Amortization of energy contract assets and liabilities	5	10
Nuclear fuel	513	569
ARO accretion	248	242
Total depreciation, amortization and accretion	1,580	1,735
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	62	100
Provision for uncollectible accounts	12	28
Other decommissioning-related activity	(261)	(61)
Energy-related options	43	(7)
Amortization of rate stabilization deferral	0	0
Amortization of operating ROU asset	78
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	439	406
Amortization of regulatory assets	69	53
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	508	459
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	47	88
Provision for uncollectible accounts	16	18
Amortization of rate stabilization deferral	0	0
Discrete impacts from EIMA and FEJA	24	14
Amortization of operating ROU asset	1
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	149	135
Amortization of regulatory assets	15	14
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	164	149
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	5	10
Provision for uncollectible accounts	10	11
Amortization of rate stabilization deferral	0	0
Amortization of operating ROU asset	0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	173	164
Amortization of regulatory assets	79	84
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	252	248
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	29	29
Provision for uncollectible accounts	4	5
Amortization of rate stabilization deferral	0	0
Amortization of operating ROU asset	15
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	266	236
Amortization of regulatory assets	103	127
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	369	363
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	48	34
Provision for uncollectible accounts	3	15
Amortization of rate stabilization deferral	(10)	13
Amortization of operating ROU asset	17
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	117	107
Amortization of regulatory assets	69	81
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	186	188
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	12	8
Provision for uncollectible accounts	2	7
Amortization of rate stabilization deferral	(8)	10
Amortization of operating ROU asset	4
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	71	64
Amortization of regulatory assets	20	24
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	91	88
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	8	3
Provision for uncollectible accounts	1	2
Amortization of rate stabilization deferral	(2)	3
Amortization of operating ROU asset	5
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment	57	47
Amortization of regulatory assets	14	22
Amortization of intangible assets, net	0	0
ARO accretion	0	0
Total depreciation, amortization and accretion	71	69
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs	8	6
Provision for uncollectible accounts	0	5
Amortization of rate stabilization deferral	0	$ 0
Amortization of operating ROU asset	$ 2