Regulatory Matters - Schedule of Completed Rate Cases (Details) - USD ($) $ in Millions	Jul. 14, 2021	Jun. 28, 2021	Jun. 22, 2021	Jun. 08, 2021	Mar. 31, 2021	Feb. 26, 2021	Dec. 16, 2020	Dec. 09, 2020	Sep. 30, 2020	Sep. 11, 2020	Jun. 01, 2020	Apr. 16, 2020
Commonwealth Edison Co [Member] | Illinois 2020 Electric Distribution Base Rate Case [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Requested Revenue Requirement Increase (Decrease)												$ (11)
Approved Revenue Requirement Increase (Decrease)								$ (14)
Approved Return on Equity, Percentage								8.38%
Public Utilities Requested Rate Increase (Decrease), Prior Year Annual Reconciliation								$ (64)
Public Utilities, Approved Equity Capital Structure, Percentage								6.28%
Basis points for ComEd's Revenue Requirement								580
Commonwealth Edison Co [Member] | Illinois 2020 Electric Distribution Base Rate Case [Member] | 2021
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)								$ 50
PECO Energy Co [Member] | Pennsylvania 2020 Natural Gas Distribution Base Rate Case
Regulatory Matters Completed Rate Cases [Line Items]
Requested Revenue Requirement Increase (Decrease)									$ 69
Approved Revenue Requirement Increase (Decrease)			$ 29
Approved Return on Equity, Percentage			10.24%
Baltimore Gas and Electric Company [Member] | Maryland 2020 Electric Distribution Base Rate Case [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount										$ 203
Approved Revenue Requirement Increase (Decrease)							$ 140
Approved Return on Equity, Percentage							9.50%
Baltimore Gas and Electric Company [Member] | Maryland 2020 Electric Distribution Base Rate Case [Member] | 2021
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)							$ 59
Baltimore Gas and Electric Company [Member] | Maryland 2020 Electric Distribution Base Rate Case [Member] | 2022
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)							39
Baltimore Gas and Electric Company [Member] | Maryland 2020 Electric Distribution Base Rate Case [Member] | 2023
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)							42
Baltimore Gas and Electric Company [Member] | Maryland 2020 Gas Distribution Base Rate Case [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount										$ 108
Approved Revenue Requirement Increase (Decrease)							$ 74
Approved Return on Equity, Percentage							9.65%
Baltimore Gas and Electric Company [Member] | Maryland 2020 Gas Distribution Base Rate Case [Member] | 2021
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)							$ 53
Baltimore Gas and Electric Company [Member] | Maryland 2020 Gas Distribution Base Rate Case [Member] | 2022
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)							11
Baltimore Gas and Electric Company [Member] | Maryland 2020 Gas Distribution Base Rate Case [Member] | 2023
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)							$ 10
Potomac Electric Power Company [Member] | Maryland 2020 Electric Distribution Base Rate Case [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount					$ 104
Approved Revenue Requirement Increase (Decrease)		$ 52
Approved Return on Equity, Percentage		9.55%
Potomac Electric Power Company [Member] | Maryland 2020 Electric Distribution Base Rate Case [Member] | March 31, 2022
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)		$ 21
Potomac Electric Power Company [Member] | Maryland 2020 Electric Distribution Base Rate Case [Member] | March 31, 2023
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)		16
Potomac Electric Power Company [Member] | Maryland 2020 Electric Distribution Base Rate Case [Member] | March 31, 2024
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)		$ 15
Potomac Electric Power Company [Member] | District of Columbia 2019 Electric Distribution Base Rate Case [Member]
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											$ 136
Approved Revenue Requirement Increase (Decrease)				$ 109
Approved Return on Equity, Percentage				9.275%
Potomac Electric Power Company [Member] | District of Columbia 2019 Electric Distribution Base Rate Case [Member] | 2021
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)				$ 42
Potomac Electric Power Company [Member] | District of Columbia 2019 Electric Distribution Base Rate Case [Member] | 2021 | Offsets
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)				(22)
Potomac Electric Power Company [Member] | District of Columbia 2019 Electric Distribution Base Rate Case [Member] | 2022
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)				67
Potomac Electric Power Company [Member] | District of Columbia 2019 Electric Distribution Base Rate Case [Member] | 2022 | Offsets
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)				$ (40)
Atlantic City Electric Company [Member] | New Jersey 2020 Electric Distribution Base Rate Case
Regulatory Matters Completed Rate Cases [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount						$ 67
Approved Revenue Requirement Increase (Decrease)	$ 41
Approved Return on Equity, Percentage	9.60%
Atlantic City Electric Company [Member] | New Jersey 2020 Electric Distribution Base Rate Case | Tax Benefits
Regulatory Matters Completed Rate Cases [Line Items]
Approved Revenue Requirement Increase (Decrease)	$ 11