Variable Interest Entities - Carrying Amounts and Classification of Consolidated VIE Assets and Liabilities (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Current assets	[1]	$ 744	$ 662
Noncurrent assets	[1]	9,234	9,317
Total assets	[1]	9,978	9,979
Current liabilities	[1]	268	308
Noncurrent liabilities	[1]	3,284	3,316
Total liabilities	[1]	3,552	3,624
Exelon Generation Co L L C [Member]
Variable Interest Entity [Line Items]
Current assets		735	652
Noncurrent assets		9,206	9,286
Total assets		9,941	9,938
Current liabilities		238	272
Noncurrent liabilities		3,226	3,250
Total liabilities		3,464	3,522
Pepco Holdings LLC [Member]
Variable Interest Entity [Line Items]
Current assets	[1]	9	10
Noncurrent assets	[1]	28	31
Total assets	[1]	37	41
Current liabilities	[1]	30	36
Noncurrent liabilities	[1]	58	66
Total liabilities	[1]	88	102
Atlantic City Electric Company [Member]
Variable Interest Entity [Line Items]
Current assets		5	6
Noncurrent assets		20	23
Total assets		25	29
Current liabilities		26	32
Noncurrent liabilities		50	58
Total liabilities		$ 76	$ 90

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