Related Party Transactions - Current Receivables From/Payables To Affiliates (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	$ 5	$ 5
Related Party Transaction, Due from (to) Related Party, Current	544	528
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	153	190
Accounts Payable, Related Parties, Current	107	117
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	78	78
Due to Related Parties, Current	50	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	11	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	3	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	6	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	25	9
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	22	28
Accounts Payable, Related Parties, Current	96	103
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	28	41
Related Party Transaction, Due from (to) Related Party, Current	13	27
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	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	2	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	1	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	5	1
Commonwealth Edison Co [Member] | Affiliated Entities [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	146	140
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	2	1
Accounts Payable, Related Parties, Current	50	55
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	2	1
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	3	1
Accounts Payable, Related Parties, Current	61	66
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	1	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	2	1
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	8	1
Accounts Payable, Related Parties, Current	104	98
Pepco Holdings LLC [Member] | Affiliated Entities [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	15	14
Potomac Electric Power Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	2	0
Accounts Payable, Related Parties, Current	55	66
Potomac Electric Power Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Potomac Electric Power Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Potomac Electric Power Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Potomac Electric Power Company [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Potomac Electric Power Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Potomac Electric Power Company [Member] | Delmarva Power and Light Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Potomac Electric Power Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Potomac Electric Power Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	2
Delmarva Power & Light Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	1	0
Accounts Payable, Related Parties, Current	36	32
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	6	4
Accounts Payable, Related Parties, Current	31	25
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	6	1
Business Services Company [Member]
Related Party Transaction [Line Items]
Receivables from affiliates, current	271	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	72	67
Business Services Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	59	54
Business Services Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	28	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	47	34
Business Services Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	4	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	25	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	21	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	15	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]
Receivables from affiliates, current	33	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	14	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	10	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	9	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]
Receivables from affiliates, current	51	51
Accounts Payable, Related Parties, Current	43	13
Other Legal Entities [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	22	23
Other Legal Entities [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	9	8
Other Legal Entities [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	4	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	3	4
Other Legal Entities [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	11	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	0	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	1	$ 1
Delmarva Power & Light Co
Related Party Transaction [Line Items]
Receivables from affiliates, current	1
Delmarva Power & Light Co | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Delmarva Power & Light Co | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Delmarva Power & Light Co | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Delmarva Power & Light Co | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Delmarva Power & Light Co | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Delmarva Power & Light Co | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Delmarva Power & Light Co | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0
Delmarva Power & Light Co | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 1