Supplemental Financial Information - Cash Flow (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2018
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			$ 2,803	$ 2,829
Amortization of regulatory assets			390	412
Amortization of intangible assets, net			44	43
Amortization of energy contract assets and liabilities			14	8
Nuclear fuel			771	852
ARO accretion			371	367
Total depreciation, amortization and accretion			4,393	4,511
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			324	435
Provision for uncollectible accounts			89	133
Other decommissioning-related activity			(400)	(39)
Energy-related options			21	4
Amortization of rate stabilization deferral			(8)	0
Discrete impacts from EIMA and FEJA			80	27
Long-term incentive plan			33	84
Amortization of operating ROU asset			193
Change in environmental liabilities			23
Asset retirement costs	$ (300)	$ 330		20
Exelon Generation Co L L C [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			1,184	1,347
Amortization of regulatory assets			0	0
Amortization of intangible assets, net			37	36
Amortization of energy contract assets and liabilities			14	8
Nuclear fuel			771	852
ARO accretion			371	365
Total depreciation, amortization and accretion			2,377	2,608
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			98	151
Provision for uncollectible accounts			20	38
Other decommissioning-related activity			(400)	(39)
Energy-related options			21	4
Amortization of rate stabilization deferral			0	0
Amortization of operating ROU asset			138
Change in environmental liabilities			0
Asset retirement costs	$ (300)	$ 330		0
Commonwealth Edison Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			661	613
Amortization of regulatory assets			106	83
Amortization of intangible assets, net			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			767	696
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			70	133
Provision for uncollectible accounts			26	30
Amortization of rate stabilization deferral			0	0
Discrete impacts from EIMA and FEJA			80	27
Amortization of operating ROU asset			2
Change in environmental liabilities			0
Asset retirement costs				0
PECO Energy Co [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			225	204
Amortization of regulatory assets			22	20
Amortization of intangible assets, net			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			247	224
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			9	14
Provision for uncollectible accounts			22	25
Amortization of rate stabilization deferral			0	0
Amortization of operating ROU asset			0
Change in environmental liabilities			0
Asset retirement costs				0
Baltimore Gas and Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			263	249
Amortization of regulatory assets			105	109
Amortization of intangible assets, net			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			368	358
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			45	43
Provision for uncollectible accounts			5	6
Amortization of rate stabilization deferral			0	0
Amortization of operating ROU asset			23
Change in environmental liabilities			0
Asset retirement costs				0
Pepco Holdings LLC [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			405	355
Amortization of regulatory assets			157	200
Amortization of intangible assets, net			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			562	555
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			71	51
Provision for uncollectible accounts			16	32
Amortization of rate stabilization deferral			(8)	0
Amortization of operating ROU asset			26
Change in environmental liabilities			23
Asset retirement costs				20
Potomac Electric Power Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			178	161
Amortization of regulatory assets			103	125
Amortization of intangible assets, net			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			281	286
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			19	10
Provision for uncollectible accounts			7	12
Amortization of rate stabilization deferral			(9)	0
Amortization of operating ROU asset			6
Change in environmental liabilities			23
Asset retirement costs				22
Delmarva Power and Light Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			109	97
Amortization of regulatory assets			29	38
Amortization of intangible assets, net			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			138	135
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			11	5
Provision for uncollectible accounts			2	6
Amortization of rate stabilization deferral			1	0
Amortization of operating ROU asset			7
Change in environmental liabilities			0
Asset retirement costs				(1)
Atlantic City Electric Company [Member]
Depreciation, Amortization and Accretion [Abstract]
Property, plant and equipment			89	70
Amortization of regulatory assets			25	37
Amortization of intangible assets, net			0	0
ARO accretion			0	0
Total depreciation, amortization and accretion			114	107
Other Non-Cash Operating Activities [Abstract]
Pension and non-pension postretirement benefit costs			12	10
Provision for uncollectible accounts			6	14
Amortization of rate stabilization deferral			0	0
Amortization of operating ROU asset			4
Change in environmental liabilities			$ 0
Asset retirement costs				$ (1)