Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Supplemental Statement of Operations Information [Line Items]
Operating lease income	$ 30	$ 30	$ 47	$ 48
Variable lease income	71	76	208	225
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	263	50	698	127
Net realized income on NDT funds - Non-regulatory agreement units	102	23	392	127
Net unrealized gains on NDT funds - Regulatory agreement units	(195)	398	84	111
Net unrealized gains on NDT funds - Non-regulatory agreement units	(88)	254	38	1
Regulatory offset to NDT fund-related activities	(38)	(359)	(607)	(192)
Decommissioning-related activities	44	366	605	174
AFUDC - Equity	36	27	99	76
Non-service net periodic benefit cost	19	15	64	38
Unrealized Gain (Loss) on Investments	(179)		(83)
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Operating lease income	29	28	44	43
Variable lease income	71	76	207	224
Decommissioning-Related Activities [Abstract]
Net realized income on NDT funds - Regulatory agreement units	263	50	698	127
Net realized income on NDT funds - Non-regulatory agreement units	102	23	392	127
Net unrealized gains on NDT funds - Regulatory agreement units	(195)	398	84	111
Net unrealized gains on NDT funds - Non-regulatory agreement units	(88)	254	38	1
Regulatory offset to NDT fund-related activities	(38)	(359)	(607)	(192)
Decommissioning-related activities	44	366	605	174
AFUDC - Equity	0	0	0	0
Non-service net periodic benefit cost	0	0	0	0
Unrealized Gain (Loss) on Investments	(179)		(83)
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	10	7	23	22
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	7	5	19	12
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	21	16
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	3	3
Variable lease income	0	0	1	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	9	36	26
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	9	7	30	20
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	3	3
Variable lease income	0	0	1	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	2	1	4	3
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	3
Non-service net periodic benefit cost	0	$ 0	0	$ 0
Unrealized Gain (Loss) on Investments	$ 0		$ 0