Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Current assets	$ 649	$ 938
Noncurrent assets	9,204	9,071
Total assets	9,853	10,009
Current liabilities	715	274
Noncurrent liabilities	2,861	3,280
Total liabilities	3,576	3,554
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets	646	931
Noncurrent assets	9,184	9,045
Total assets	9,830	9,976
Current liabilities	694	252
Noncurrent liabilities	2,827	3,233
Total liabilities	3,521	3,485
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets	3	7
Noncurrent assets	20	26
Total assets	23	33
Current liabilities	21	22
Noncurrent liabilities	34	47
Total liabilities	55	69
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets	2	4
Noncurrent assets	17	19
Total assets	19	23
Current liabilities	20	19
Noncurrent liabilities	31	40
Total liabilities	$ 51	$ 59