Schedule II - Valuation and Qualifying Accounts Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 319	$ 322	$ 334
Charged to Costs and Expenses	119	159	126
Charged to Other Accounts	26	35	27
Deductions	170	197	165
Balance at End of Period	294	319	322
Deferred Tax Valuation Allowance [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	35	37	20
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	(9)	5	17
Deductions	0	7	0
Balance at End of Period	26	35	37
Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	156	174	113
Charged to Costs and Expenses	6	25	56
Charged to Other Accounts	0	(31)	10
Deductions	7	12	5
Balance at End of Period	155	156	174
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	104	114	91
Charged to Costs and Expenses	27	44	34
Charged to Other Accounts	(11)	4	0
Deductions	39	58	11
Balance at End of Period	81	104	114
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	26	23	9
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	(2)	3	14
Deductions	0	0	0
Balance at End of Period	24	26	23
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	145	166	106
Charged to Costs and Expenses	0	20	51
Charged to Other Accounts	0	(32)	9
Deductions	2	9	0
Balance at End of Period	143	145	166
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	81	73	70
Charged to Costs and Expenses	35	44	39
Charged to Other Accounts	20	23	20
Deductions	57	59	56
Balance at End of Period	79	81	73
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	6	5	4
Charged to Costs and Expenses	6	3	3
Charged to Other Accounts	0	1	1
Deductions	5	3	3
Balance at End of Period	7	6	5
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	61	56	61
Charged to Costs and Expenses	31	33	26
Charged to Other Accounts	3	3	4
Deductions	33	31	35
Balance at End of Period	62	61	56
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	0	0	0
Charged to Other Accounts	0	0	0
Deductions	0	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	13	15
Balance at End of Period	9	13	15
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	20	24	32
Charged to Costs and Expenses	8	10	8
Charged to Other Accounts	7	(2)	(3)
Deductions	18	12	13
Balance at End of Period	17	20	24
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	0	0	0
Deductions	0	0	0
Balance at End of Period	1	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	0	0
Charged to Costs and Expenses	0	1	0
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Period	1	1	0
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	55	80
Charged to Costs and Expenses	17	28	19
Charged to Other Accounts	7	7	6
Deductions	24	37	50
Balance at End of Period	53	53	55
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	8	13	10
Charged to Costs and Expenses	0	0	0
Charged to Other Accounts	(8)	2	3
Deductions	0	7	0
Balance at End of Period	0	8	13
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	2	2	2
Charged to Costs and Expenses	1	0	2
Charged to Other Accounts	0	0	0
Deductions	0	0	2
Balance at End of Period	3	2	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	21	21	29
Charged to Costs and Expenses	7	11	8
Charged to Other Accounts	2	3	2
Deductions	10	14	18
Balance at End of Period	20	21	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	1
Charged to Other Accounts	0	0	0
Deductions	0	0	1
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	13	16	24
Charged to Costs and Expenses	4	6	3
Charged to Other Accounts	3	2	2
Deductions	5	11	13
Balance at End of Period	15	13	16
Delmarva Power & Light Company [Member] | Reserve for Obsolete Materials [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	0	0	0
Charged to Costs and Expenses	0	0	1
Charged to Other Accounts	0	0	0
Deductions	0	0	1
Balance at End of Period	0	0	0
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	19	18	27
Charged to Costs and Expenses	5	11	8
Charged to Other Accounts	2	2	2
Deductions	8	12	19
Balance at End of Period	18	19	18
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	0	0	0
Balance at End of Period	$ 1	$ 1	$ 1