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Cover Page - USD ($)
12 Months Ended
Dec. 31, 2020
Jan. 31, 2021
Jun. 30, 2020
Document Type 10-K    
Amendment Flag false    
Document Annual Report true    
Document Period End Date Dec. 31, 2020    
Document Transition Report false    
Entity File Number 001-16169    
Entity Registrant Name EXELON CORPORATION    
Entity Incorporation, State or Country Code PA    
Entity Tax Identification Number 23-2990190    
Entity Address, Address Line One 10 South Dearborn Street    
Entity Address, Address Line Two P.O. Box 805379    
Entity Address, City or Town Chicago    
Entity Address, State or Province IL    
Entity Address, Postal Zip Code 60680-5379    
City Area Code (800)    
Local Phone Number 483-3220    
Title of 12(b) Security Common Stock, without par value    
Trading Symbol EXC    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 35,402,501,369
Entity Common Stock Shares Outstanding   976,337,799  
Documents Incorporated by Reference [Text Block] Portions of the Exelon Proxy Statement for the 2020 Annual Meeting of Shareholders and the Commonwealth Edison Company 2020 Information Statement are incorporated by reference in Part III.    
Entity Central Index Key 0001109357    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Exelon Generation Co L L C [Member]      
Entity File Number 333-85496    
Entity Registrant Name EXELON GENERATION COMPANY, LLC    
Entity Incorporation, State or Country Code PA    
Entity Tax Identification Number 23-3064219    
Entity Address, Address Line One 300 Exelon Way    
Entity Address, City or Town Kennett Square    
Entity Address, State or Province PA    
Entity Address, Postal Zip Code 19348-2473    
City Area Code (610)    
Local Phone Number 765-5959    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Central Index Key 0001168165    
Commonwealth Edison Co [Member]      
Entity File Number 001-01839    
Entity Registrant Name COMMONWEALTH EDISON COMPANY    
Entity Incorporation, State or Country Code IL    
Entity Tax Identification Number 36-0938600    
Entity Address, Address Line One 440 South LaSalle Street    
Entity Address, City or Town Chicago    
Entity Address, State or Province IL    
Entity Address, Postal Zip Code 60605-1028    
City Area Code (312)    
Local Phone Number 394-4321    
Title of 12(g) Security Common Stock Purchase Warrants (1971 Warrants and Series B Warrants)    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Common Stock Shares Outstanding   127,021,370  
Entity Central Index Key 0000022606    
PECO Energy Co [Member]      
Entity File Number 000-16844    
Entity Registrant Name PECO ENERGY COMPANY    
Entity Incorporation, State or Country Code PA    
Entity Tax Identification Number 23-0970240    
Entity Address, Address Line One P.O. Box 8699    
Entity Address, Address Line Two 2301 Market Street    
Entity Address, City or Town Philadelphia    
Entity Address, State or Province PA    
Entity Address, Postal Zip Code 19101-8699    
City Area Code (215)    
Local Phone Number 841-4000    
Title of 12(b) Security Cumulative Preferred Security, Series D,    
Trading Symbol EXC/28    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Common Stock Shares Outstanding   170,478,507  
Entity Central Index Key 0000078100    
Baltimore Gas and Electric Company [Member]      
Entity File Number 001-01910    
Entity Registrant Name BALTIMORE GAS AND ELECTRIC COMPANY    
Entity Incorporation, State or Country Code MD    
Entity Tax Identification Number 52-0280210    
Entity Address, Address Line One 2 Center Plaza    
Entity Address, Address Line Two 110 West Fayette Street    
Entity Address, City or Town Baltimore    
Entity Address, State or Province MD    
Entity Address, Postal Zip Code 21201-3708    
City Area Code (410)    
Local Phone Number 234-5000    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Common Stock Shares Outstanding   1,000  
Entity Central Index Key 0000009466    
Pepco Holdings LLC [Member]      
Entity File Number 001-31403    
Entity Registrant Name PEPCO HOLDINGS LLC    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 52-2297449    
Entity Address, Address Line One 701 Ninth Street, N.W.    
Entity Address, City or Town Washington, District of Columbia    
Entity Address, Postal Zip Code 20068    
City Area Code (202)    
Local Phone Number 872-2000    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Central Index Key 0001135971    
Potomac Electric Power Company [Member]      
Entity File Number 001-01072    
Entity Registrant Name POTOMAC ELECTRIC POWER COMPANY    
Entity Tax Identification Number 53-0127880    
Entity Address, Address Line One 701 Ninth Street, N.W.    
Entity Address, City or Town Washington, District of Columbia    
Entity Address, Postal Zip Code 20068    
City Area Code (202)    
Local Phone Number 872-2000    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Common Stock Shares Outstanding   100  
Entity Central Index Key 0000079732    
Delmarva Power & Light Company [Member]      
Entity File Number 001-01405    
Entity Registrant Name DELMARVA POWER & LIGHT COMPANY    
Entity Tax Identification Number 51-0084283    
Entity Address, Address Line One 500 North Wakefield Drive    
Entity Address, City or Town Newark    
Entity Address, State or Province DE    
Entity Address, Postal Zip Code 19702    
City Area Code (202)    
Local Phone Number 872-2000    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Common Stock Shares Outstanding   1,000  
Entity Central Index Key 0000027879    
Atlantic City Electric Company [Member]      
Entity File Number 001-03559    
Entity Registrant Name ATLANTIC CITY ELECTRIC COMPANY    
Entity Incorporation, State or Country Code NJ    
Entity Tax Identification Number 21-0398280    
Entity Address, Address Line One 500 North Wakefield Drive    
Entity Address, City or Town Newark    
Entity Address, State or Province DE    
Entity Address, Postal Zip Code 19702    
City Area Code (202)    
Local Phone Number 872-2000    
Entity Well-known Seasoned Issuer No    
Entity Voluntary Filers No    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Common Stock Shares Outstanding   8,546,017  
Entity Central Index Key 0000008192    
VIRGINIA | Potomac Electric Power Company [Member]      
Entity Incorporation, State or Country Code VA    
VIRGINIA | Delmarva Power & Light Company [Member]      
Entity Incorporation, State or Country Code VA    
DELAWARE | Delmarva Power & Light Company [Member]      
Entity Incorporation, State or Country Code DE    
DISTRICT OF COLUMBIA | Potomac Electric Power Company [Member]      
Entity Incorporation, State or Country Code DC