Related Party Transactions - Current Receivables From/Payables To Affiliates (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	$ 472	$ 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	128	117
Accounts Receivable, Related Parties, Current	167	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	69	78
Due to Related Parties, Current	27	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	25	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	22	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	29	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	1	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	12	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	87	103
Accounts Receivable, Related Parties, Current	18	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	17	27
Accounts Payable, Related Parties, Current	42	41
Commonwealth Edison Co [Member] | Affiliated Entity [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	114	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	51	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	52	66
Accounts Receivable, Related Parties, Current	1	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	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	0	1
Pepco Holdings LLC [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	82	98
Accounts Receivable, Related Parties, Current	1	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	55	66
Delmarva Power and Light Company [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	21	32
Accounts Receivable, Related Parties, Current	1	0
Delmarva Power and Light Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	1	0
Delmarva Power and Light Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Delmarva Power and Light Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Delmarva Power and Light 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
Delmarva Power and Light Company [Member] | Pepco Holdings LLC Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Delmarva Power and Light Company [Member] | Potomac Electric Power Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Delmarva Power and Light Company [Member] | Atlantic City Electric Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Delmarva Power and Light Company [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	0	0
Atlantic City Electric Company [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties, Current	27	25
Accounts Receivable, Related Parties, Current	4	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	3	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	181	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	67	67
Business Services Company [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	42	54
Business Services Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	19	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	27	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	11	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	7	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	5	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	30	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	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]
Accounts Payable, Related Parties, Current	11	13
Accounts Receivable, Related Parties, Current	70	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	43	23
Other Legal Entities [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	3	8
Other Legal Entities [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Due from (to) Related Party, Current	7	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	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	$ 1	$ 1