Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Supplemental Statement of Operations Information [Line Items]
Operating lease income	$ 13	$ 14	$ 17	$ 18
Variable lease income	74	80	137	149
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	144	30	435	77
Net realized income on NDT funds - Non-regulatory agreement units	87	23	290	104
Net unrealized gains on NDT funds - Regulatory agreement units	361	645	279	(287)
Net unrealized gains on NDT funds - Non-regulatory agreement units	193	452	126	(253)
Regulatory offset to NDT fund-related activities	(402)	(542)	(569)	167
Decommissioning-related activities	383	608	561	(192)
AFUDC - Equity	35	26	64	49
Non-service net periodic benefit cost	26	14	46	24
Unrealized Gain (Loss) on Investments	119		96
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Operating lease income	12	12	15	15
Variable lease income	74	79	137	148
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	144	30	435	77
Net realized income on NDT funds - Non-regulatory agreement units	87	23	290	104
Net unrealized gains on NDT funds - Regulatory agreement units	361	645	279	(287)
Net unrealized gains on NDT funds - Non-regulatory agreement units	193	452	126	(253)
Regulatory offset to NDT fund-related activities	(402)	(542)	(569)	167
Decommissioning-related activities	383	608	561	(192)
AFUDC - Equity	0	0	0	0
Non-service net periodic benefit cost	0	0	0	0
Unrealized Gain (Loss) on Investments	119		96
Commonwealth Edison Co [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Non-regulatory agreement units	0	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0	0
Decommissioning-related activities	0	0	0	0
AFUDC - Equity	9	8	13	14
Non-service net periodic benefit cost	0	0	0	0
Unrealized Gain (Loss) on Investments	0		0
PECO Energy Co [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Non-regulatory agreement units	0	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0	0
Decommissioning-related activities	0	0	0	0
AFUDC - Equity	6	4	12	7
Non-service net periodic benefit cost	0	0	0	0
Unrealized Gain (Loss) on Investments	0		0
Baltimore Gas and Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Non-regulatory agreement units	0	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0	0
Decommissioning-related activities	0	0	0	0
AFUDC - Equity	7	6	14	10
Non-service net periodic benefit cost	0	0	0	0
Unrealized Gain (Loss) on Investments	0		0
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Operating lease income	1	1	2	2
Variable lease income	0	1	0	1
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Non-regulatory agreement units	0	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0	0
Decommissioning-related activities	0	0	0	0
AFUDC - Equity	12	8	25	17
Non-service net periodic benefit cost	0	0	0	0
Unrealized Gain (Loss) on Investments	0		0
Potomac Electric Power Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Non-regulatory agreement units	0	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0	0
Decommissioning-related activities	0	0	0	0
AFUDC - Equity	10	6	20	13
Non-service net periodic benefit cost	0	0	0	0
Unrealized Gain (Loss) on Investments	0		0
Delmarva Power and Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Operating lease income	1	1	2	2
Variable lease income	0	1	0	1
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Non-regulatory agreement units	0	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0	0
Decommissioning-related activities	0	0	0	0
AFUDC - Equity	1	1	3	2
Non-service net periodic benefit cost	0	0	0	0
Unrealized Gain (Loss) on Investments	0		0
Atlantic City Electric Company [Member]
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	0	0	0	0
Net realized income on NDT funds - Non-regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Regulatory agreement units	0	0	0	0
Net unrealized gains on NDT funds - Non-regulatory agreement units	0	0	0	0
Regulatory offset to NDT fund-related activities	0	0	0	0
Decommissioning-related activities	0	0	0	0
AFUDC - Equity	1	1	2	2
Non-service net periodic benefit cost	0	$ 0	0	$ 0
Unrealized Gain (Loss) on Investments	$ 0		$ 0