Supplemental Financial Information - Summary of Other Income (Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	$ 185	$ 297	$ 506
Net realized income on NDT funds - Non-regulatory agreement units	160	363	302
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	724	795	(715)
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	391	411	(483)
Regulatory offset to NDT fund-related activities	(729)	(876)	171
Total decommissioning-related activities	731	990	(219)
AFUDC—Equity	104	85	69
Non-service net periodic benefit cost	53	13	(47)
Unrealized Gain (Loss) on Investments	186	0	0
Exelon Generation Co L L C [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	185	297	506
Net realized income on NDT funds - Non-regulatory agreement units	160	363	302
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	724	795	(715)
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	391	411	(483)
Regulatory offset to NDT fund-related activities	(729)	(876)	171
Total decommissioning-related activities	731	990	(219)
AFUDC—Equity	0	0	0
Non-service net periodic benefit cost	0	0	0
Unrealized Gain (Loss) on Investments	186	0	0
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0
Total decommissioning-related activities	0	0	0
AFUDC—Equity	29	17	19
Non-service net periodic benefit cost	0	0	0
Unrealized Gain (Loss) on Investments	0
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0
Total decommissioning-related activities	0	0	0
AFUDC—Equity	17	13	7
Non-service net periodic benefit cost	0	0	0
Unrealized Gain (Loss) on Investments	0
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0
Total decommissioning-related activities	0	0	0
AFUDC—Equity	22	21	18
Non-service net periodic benefit cost	0	0	0
Unrealized Gain (Loss) on Investments	0
Pepco Holdings LLC [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0
Total decommissioning-related activities	0	0	0
AFUDC—Equity	36	34	25
Non-service net periodic benefit cost	0	0	0
Unrealized Gain (Loss) on Investments	0
Potomac Electric Power Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0
Total decommissioning-related activities	0	0	0
AFUDC—Equity	28	25	22
Non-service net periodic benefit cost	0	0	0
Unrealized Gain (Loss) on Investments	0
Delmarva Power & Light Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0
Total decommissioning-related activities	0	0	0
AFUDC—Equity	4	4	2
Non-service net periodic benefit cost	0	0	0
Unrealized Gain (Loss) on Investments	0
Atlantic City Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Regulatory agreement units	0	0	0
Net unrealized gains (losses) on NDT funds - Non-regulatory agreement	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0
Total decommissioning-related activities	0	0	0
AFUDC—Equity	4	5	1
Non-service net periodic benefit cost	0	$ 0	$ 0
Unrealized Gain (Loss) on Investments	$ 0