Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Current assets		$ 645	$ 938
Noncurrent assets		9,235	9,071
Total assets	[1]	9,880	10,009
Current liabilities		748	274
Noncurrent liabilities		2,831	3,280
Total liabilities	[1]	3,579	3,554
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		639	931
Noncurrent assets		9,210	9,045
Total assets		9,849	9,976
Current liabilities		725	252
Noncurrent liabilities		2,790	3,233
Total liabilities		3,515	3,485
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets		6	7
Noncurrent assets		25	26
Total assets	[1]	31	33
Current liabilities		23	22
Noncurrent liabilities		41	47
Total liabilities	[1]	64	69
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		3	4
Noncurrent assets		19	19
Total assets		22	23
Current liabilities		19	19
Noncurrent liabilities		35	40
Total liabilities		$ 54	$ 59

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