Lessee - Lessee Future Minimum Operating Lease Maturity Payments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2021	$ 239
2022	177
2023	146
2024	141
2025	140
Remaining years	834
Lessee, Operating Lease, Liability, to be Paid	1,677
Interest	375
Operating Lease, Liability	1,302	$ 1,532
Exelon Generation Co L L C [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2021	145
2022	113
2023	100
2024	98
2025	99
Remaining years	640
Lessee, Operating Lease, Liability, to be Paid	1,195
Interest	288
Operating Lease, Liability	907	1,082
Commonwealth Edison Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2021	3
2022	2
2023	1
2024	1
2025	1
Remaining years	0
Lessee, Operating Lease, Liability, to be Paid	8
Interest	0
Operating Lease, Liability	8	11
PECO Energy Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2021	1
2022	0
2023	0
2024	0
2025	0
Remaining years	0
Lessee, Operating Lease, Liability, to be Paid	1
Interest	0
Operating Lease, Liability	1	1
Baltimore Gas and Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2021	46
2022	16
2023	1
2024	0
2025	0
Remaining years	18
Lessee, Operating Lease, Liability, to be Paid	81
Interest	17
Operating Lease, Liability	64	82
Pepco Holdings LLC [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2021	40
2022	39
2023	38
2024	36
2025	33
Remaining years	120
Lessee, Operating Lease, Liability, to be Paid	306
Interest	51
Operating Lease, Liability	255	285
Schedule of Lessee, Finance Lease, Liability, Maturity [Line Items]
2021	8
2022	8
2023	8
2024	8
2025	8
Remaining years	13
Finance Lease, Liability, to be Paid	53
Interest	3
Finance lease, liability	50
Potomac Electric Power Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2021	8
2022	8
2023	7
2024	6
2025	6
Remaining years	28
Lessee, Operating Lease, Liability, to be Paid	63
Interest	11
Operating Lease, Liability	52	57
Schedule of Lessee, Finance Lease, Liability, Maturity [Line Items]
2021	3
2022	3
2023	3
2024	3
2025	3
Remaining years	3
Finance Lease, Liability, to be Paid	18
Interest	1
Finance lease, liability	17
Delmarva Power & Light Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2021	11
2022	10
2023	9
2024	8
2025	7
Remaining years	35
Lessee, Operating Lease, Liability, to be Paid	80
Interest	15
Operating Lease, Liability	65	74
Schedule of Lessee, Finance Lease, Liability, Maturity [Line Items]
2021	3
2022	3
2023	3
2024	3
2025	3
Remaining years	6
Finance Lease, Liability, to be Paid	21
Interest	1
Finance lease, liability	20
Atlantic City Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2021	5
2022	4
2023	3
2024	2
2025	2
Remaining years	0
Lessee, Operating Lease, Liability, to be Paid	16
Interest	1
Operating Lease, Liability	15	$ 18
Schedule of Lessee, Finance Lease, Liability, Maturity [Line Items]
2021	2
2022	2
2023	2
2024	2
2025	2
Remaining years	4
Finance Lease, Liability, to be Paid	14
Interest	1
Finance lease, liability	$ 13

Schedule of Lessee, Finance Lease, Liability, Maturity

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[Line Items] for Schedule of Lessee, Operating Lease, Liability, Maturity

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Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918701-209980

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

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Amount of lessee's undiscounted obligation for lease payments for finance lease.

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid in remainder of current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918701-209980

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Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for finance lease.

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Amount of lessee's undiscounted obligation for lease payment for operating lease.

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Amount of lessee's undiscounted obligation for lease payment for operating lease due after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease having initial or remaining lease term in excess of one year to be paid in remainder of current fiscal year.

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Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for operating lease.

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Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

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