Variable Interest Entities Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Dec. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Current assets	[1]	$ 938	$ 662
Noncurrent assets	[1]	9,071	9,317
Total assets	[1]	10,009	9,979
Current liabilities	[1]	274	308
Noncurrent liabilities	[1]	3,280	3,316
Total liabilities	[1]	3,554	3,624
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		931	652
Noncurrent assets		9,045	9,286
Total assets		9,976	9,938
Current liabilities		252	272
Noncurrent liabilities		3,233	3,250
Total liabilities		3,485	3,522
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	7	10
Noncurrent assets	[1]	26	31
Total assets	[1]	33	41
Current liabilities	[1]	22	36
Noncurrent liabilities	[1]	47	66
Total liabilities	[1]	69	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		4	6
Noncurrent assets		19	23
Total assets		23	29
Current liabilities		19	32
Noncurrent liabilities		40	58
Total liabilities		$ 59	$ 90

[1] Includes certain purchase accounting adjustments not pushed down to the ACE standalone entity.