Related Party Transactions - Current Receivables From/Payables To Affiliates (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 423	$ 528
Accounts Payable, Related Parties, Current	5	5
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	113	117
Accounts Receivable, Related Parties, Current	109	190
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	56	78
Due to Related Parties, Current	28	37
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	17	27
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	8	28
Exelon Generation Co L L C [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Exelon Generation Co L L C [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	13	34
Exelon Generation Co L L C [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	2	7
Exelon Generation Co L L C [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	4	7
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	9	9
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	82	103
Accounts Receivable, Related Parties, Current	20	28
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	19	27
Accounts Payable, Related Parties, Current	28	41
Commonwealth Edison Co [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	110	140
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Commonwealth Edison Co [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	1
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	47	55
Accounts Receivable, Related Parties, Current	0	1
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PECO Energy Co [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PECO Energy Co [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PECO Energy Co [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PECO Energy Co [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PECO Energy Co [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	1
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	39	66
Accounts Receivable, Related Parties, Current	0	1
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Baltimore Gas and Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	1
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	71	98
Accounts Receivable, Related Parties, Current	0	1
Pepco Holdings LLC [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	13	14
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	43	66
Delmarva Power and Light Company [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	23	32
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	24	25
Accounts Receivable, Related Parties, Current	1	4
Atlantic City Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	3
Atlantic City Electric Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	1
Business Services Company [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	211	217
Business Services Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	69	67
Business Services Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	49	54
Business Services Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	24	25
Business Services Company [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	29	34
Business Services Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	3	4
Business Services Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	16	16
Business Services Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	11	10
Business Services Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	10	7
Business Services Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	31	36
PHI Service Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
PHI Service Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	12	15
PHI Service Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	9	11
PHI Service Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	10	10
PHI Service Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Other Legal Entities [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	11	13
Accounts Receivable, Related Parties, Current	51	51
Other Legal Entities [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	25	23
Other Legal Entities [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	5	8
Other Legal Entities [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	6	3
Other Legal Entities [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	2	4
Other Legal Entities [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	10	10
Other Legal Entities [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	2	1
Other Legal Entities [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	1
Other Legal Entities [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 0	$ 1