Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Current assets	[1]	$ 823	$ 662
Noncurrent assets	[1]	9,279	9,317
Total assets	[1]	10,102	9,979
Current liabilities	[1]	269	308
Noncurrent liabilities	[1]	3,292	3,316
Total liabilities	[1]	3,561	3,624
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		812	652
Noncurrent assets		9,251	9,286
Total assets		10,063	9,938
Current liabilities		236	272
Noncurrent liabilities		3,230	3,250
Total liabilities		3,466	3,522
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	11	10
Noncurrent assets	[1]	28	31
Total assets	[1]	39	41
Current liabilities	[1]	33	36
Noncurrent liabilities	[1]	62	66
Total liabilities	[1]	95	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		7	6
Noncurrent assets		20	23
Total assets		27	29
Current liabilities		29	32
Noncurrent liabilities		54	58
Total liabilities		$ 83	$ 90

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