Schedule II - Valuation and Qualifying Accounts Schedule (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 294	$ 319	$ 322
Charged to Costs and Expenses	240	119	159
Charged to Other Accounts	(18)	26	35
Deductions	79	170	197
Balance at End of Period	437	294	319
Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	26	35	37
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	1	(9)	5
Deductions	0	0	7
Balance at End of Period	27	26	35
Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	155	156	174
Charged to Costs and Expenses	128	6	25
Charged to Other Accounts	(1)	0	(31)
Deductions	6	7	12
Balance at End of Period	276	155	156
Exelon Generation Co L L C [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	81	104	114
Charged to Costs and Expenses	12	27	44
Charged to Other Accounts	(56)	(11)	4
Deductions	5	39	58
Balance at End of Period	32	81	104
Exelon Generation Co L L C [Member] | Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	24	26	23
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	(1)	(2)	3
Deductions	0	0	0
Balance at End of Period	23	24	26
Exelon Generation Co L L C [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	143	145	166
Charged to Costs and Expenses	123	0	20
Charged to Other Accounts	(1)	0	(32)
Deductions	0	2	9
Balance at End of Period	265	143	145
Commonwealth Edison Co [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	79	81	73
Charged to Costs and Expenses	54	35	44
Charged to Other Accounts	13	20	23
Deductions	28	57	59
Balance at End of Period	118	79	81
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	7	6	5
Charged to Costs and Expenses	3	6	3
Charged to Other Accounts	0	0	1
Deductions	4	5	3
Balance at End of Period	6	7	6
PECO Energy Co [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	62	61	56
Charged to Costs and Expenses	76	31	33
Charged to Other Accounts	6	3	3
Deductions	20	33	31
Balance at End of Period	124	62	61
PECO Energy Co [Member] | Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	0
Charged to Costs and Expenses	0
Charged to Other Accounts	1
Deductions	0
Balance at End of Period	1	0
PECO Energy Co [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	2	2	2
Charged to Costs and Expenses	1	0	0
Charged to Other Accounts	0	0	0
Deductions	1	0	0
Balance at End of Period	2	2	2
PECO Energy Co [Member] | SEC Schedule, 12-09, Allowance, Notes Receivable [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	9	13
Balance at End of Period	5	9	13
Baltimore Gas and Electric Company [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	17	20	24
Charged to Costs and Expenses	31	8	10
Charged to Other Accounts	6	7	(2)
Deductions	10	18	12
Balance at End of Period	44	17	20
Baltimore Gas and Electric Company [Member] | Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1	1	1
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	(1)	0	0
Deductions	0	0	0
Balance at End of Period	0	1	1
Baltimore Gas and Electric Company [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1	1	0
Charged to Costs and Expenses	0	0	1
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	1	1	1
Pepco Holdings LLC [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	53	53	55
Charged to Costs and Expenses	69	17	28
Charged to Other Accounts	13	7	7
Deductions	16	24	37
Balance at End of Period	119	53	53
Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	0	8	13
Charged to Costs and Expenses		0	0
Charged to Other Accounts		(8)	2
Deductions		0	7
Balance at End of Period		0	8
Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	3	2	2
Charged to Costs and Expenses	0	1	0
Charged to Other Accounts	0	0	0
Deductions	1	0	0
Balance at End of Period	2	3	2
Potomac Electric Power Company [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	20	21	21
Charged to Costs and Expenses	25	7	11
Charged to Other Accounts	5	2	3
Deductions	5	10	14
Balance at End of Period	45	20	21
Potomac Electric Power Company [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1	1	1
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	1	1	1
Delmarva Power & Light Company [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	15	13	16
Charged to Costs and Expenses	16	4	6
Charged to Other Accounts	4	3	2
Deductions	4	5	11
Balance at End of Period	31	15	13
Atlantic City Electric Company [Member] | SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	18	19	18
Charged to Costs and Expenses	28	5	11
Charged to Other Accounts	4	2	2
Deductions	7	8	12
Balance at End of Period	43	18	19
Atlantic City Electric Company [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1	1	1
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	0	0	0
Deductions	1	0	0
Balance at End of Period	$ 0	$ 1	$ 1