Asset Retirement Obligations - Non-Nuclear Asset Retirement Obligations Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	$ 500	$ 491	$ 489
Asset Retirement Obligation, Revision of Estimate			20
Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	500	491	489
Asset Retirement Obligation, Revision of Estimate			0
Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	0	0	0
Asset Retirement Obligation, Revision of Estimate			0
PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	0	0	0
Asset Retirement Obligation, Revision of Estimate			0
Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	0	0	0
Asset Retirement Obligation, Revision of Estimate			0
Pepco Holdings LLC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	0	0	0
Asset Retirement Obligation, Revision of Estimate			20
Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	0	0	0
Asset Retirement Obligation, Revision of Estimate			22
Delmarva Power & Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	0	0	0
Asset Retirement Obligation, Revision of Estimate			(1)
Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Accretion expense	0	0	0
Asset Retirement Obligation, Revision of Estimate			(1)
Nonnuclear Decommissioning Asset Retirement Obligation [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	460	471
Development Projects	1	2
Accretion expense	16	16
Sale of Oyster Creek	(4)	(42)
Payments	(9)	(4)
Asset Retirement Obligation, Revision of Estimate	7	17
ARO ending balance	461	460	471
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate	10
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| Exelon Generation Co L L C [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	216	238
Development Projects	1	2
Accretion expense	11	12
Sale of Oyster Creek	(4)	(42)
Payments	(4)	(1)
Asset Retirement Obligation, Revision of Estimate	2	7
ARO ending balance	212	216	238
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| Exelon Generation Co L L C [Member] \| Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation, Revision of Estimate	10
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| Commonwealth Edison Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	129	121
Development Projects	0	0
Accretion expense	1	1
Sale of Oyster Creek	0	0
Payments	(1)	(1)
Asset Retirement Obligation, Revision of Estimate	0	8
ARO ending balance	129	129	121
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| PECO Energy Co [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	28	28
Development Projects	0	0
Accretion expense	1	1
Sale of Oyster Creek	0	0
Payments	(2)	(1)
Asset Retirement Obligation, Revision of Estimate	2	0
ARO ending balance	29	28	28
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| Baltimore Gas and Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	23	25
Development Projects	0	0
Accretion expense	1	1
Sale of Oyster Creek	0	0
Payments	(2)	(1)
Asset Retirement Obligation, Revision of Estimate	1	(2)
ARO ending balance	23	23	25
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| Pepco Holdings LLC [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	57	52
Development Projects	0	0
Accretion expense	1	1
Sale of Oyster Creek	0	0
Payments	0	0
Asset Retirement Obligation, Revision of Estimate	1	4
ARO ending balance	59	57	52
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| Potomac Electric Power Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	41	37
Development Projects	0	0
Accretion expense	1	1
Sale of Oyster Creek	0	0
Payments	0	0
Asset Retirement Obligation, Revision of Estimate	(3)	3
ARO ending balance	39	41	37
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| Delmarva Power & Light Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	12	11
Development Projects	0	0
Accretion expense	0	0
Sale of Oyster Creek	0	0
Payments	0	0
Asset Retirement Obligation, Revision of Estimate	2	1
ARO ending balance	14	12	11
Nonnuclear Decommissioning Asset Retirement Obligation [Member] \| Atlantic City Electric Company [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
ARO beginning balance	4	4
Development Projects	0	0
Accretion expense	0	0
Sale of Oyster Creek	0	0
Payments	0	0
Asset Retirement Obligation, Revision of Estimate	2	0
ARO ending balance	$ 6	$ 4	$ 4

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 45
-Paragraph 1
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- Definition

Amount of cash paid during the period to settle an asset retirement obligation. Amounts paid to settle an asset retirement obligation are generally included in the operating section of the Statement of Cash Flows.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 17
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3367-108585

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Amount of asset retirement obligations incurred during the period.

+ References

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 35
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-SubTopic 20
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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